PHYSICAL CHEMISTRY

this is the branch of science which unites physics and chemistry. whilst chemistry was originally occupied by the changes which matter undergoes in composition, classical physics describes the properties of relatively few substances, the materials, as far as composition is concerned, remaining constant during a physical change. the progress of knowledge led to a more intense study of chemi- cal properties, and attempts were made to express the laws of chemical change in mathematical terms. on the other hand, physics investigated an increasing number of chemically in- dividual substances, and the department of physical chemistry developed, covering the ground where the two sciences over- lapped one another. hisrory of the science in the early days of science, chemistry and physics were not differentiated. later, the great progress of physics and the discoveries of newton accelerated the search for the laws gov- erning chemical processes. perhaps the greatest interest was aroused by the case of solution, which lies on the border between physics and chemistry. newton even tried to apply the theory of gravitation to this phenomenon, maintaining that a salt is dissolved in water if the particles of salt have a greater attrac- tion for water molecules than they have for one another. newton found that such interaction gave an insufficient explanation, and repulsion is responsible for the distribution of dissolved molecules in a solvent. in a certain sense he hereby introduced the idea of osmotic pressure, which plays an important part in modern theories. lavoisier made a strong distinction between such cases as salt or sugar dissolving in water and a metal dissolving in an 137 acid. the latter process he called dissolution. the recovery of the salt or sugar is simple, that of the metal from solution in an acid is difficult. the solution of a metal in an acid is an un- doubted chemical process, the solution of a salt in water might as well be regarded as a physical as a chemical process. lavoisier also drew attention to the fusibility of salts, and concluded that “ caloric’ and water would aid one another in dissolving matter, 7.c., solubility should increase with rise in temperature. though true in most cases, certain salts, such as calcium sulphate, exhibit decrease in solubility with increase in temperature. richter and berthollet differed from lavoisier in regarding solution as caused by chemical affinity. since the composition of a saturated solution changes with temperature, berthollet denied the law of constant proportions; the establishment of the atomic theory on an experimental basis negatived berthollet’s view. further, gay-lussac (1805) discovered that the volumes of two gases, measured under equal conditions of temperature and pressure, which unite to form a compound, bear a simple relationship to one another. this was followed by the law of avogadro (1811), according to which equal volumes of different gases, under the same conditions as to temperature and pres- sure, contain equal numbers of molecules. mathematical chemistry the kinetic theory of gases was developed on the mathe- matical side and led to estimates of molecular and atomic dimen- sions; the atomic theory scemed to have been thoroughly estab- lished. opposition to the theory recurred towards the end of the last century (wald, helm), and received some support (ostwald, le chatelier); the matter is now of purely historical interest. the analogy between the brownian movement (discovered by the english botanist, robert brown, in 1827) of small par- ticles, such as pollen grains, and the translatory motion of the molecules of a gas was eventually recognised and the mathe- matical theory worked out by von smoluchowski and einstein. convincing proof was afforded by the experiments of a number of workers, especially svedberg and perrin, and the results were used to calculate the number of molecules, n, in a gram-mol. of a gas, ¢.g., 1n 32 grammes of oxygen. the most rehable results of svedberg and his pupils is n= (6-0 0-003) x10", fletcher’s figure is very close, perrin’s value about 10% higher. rutherford, geiger and regener counted the number of a particles emitted by a given quantity of radium in a second, and dletermined the rate of decay of radium. as, according to fara- day’s law, the charge of a gramme of hydrogen ion is 96,550 coulombs, they could determine the charge of an a-particle, which is double as great as that of a @-particle, the smallest known quantity of electricity, or the atom of clectricity. ruther- ford in this manner found n=6-2x 10. dewar and boltwood found independently of each other n=7-1x10%, the exceed- ingly accurate measurements of mullikan gave the electrical atom, e, equal to (4-774 =£0-005)x1o-" electrostatic units, corresponding to n= (6-062 +0-006)10%3. from planck’s theory of heat, n=6-2x 10; the same number is arrived at from measurements of the charge of droplets con- densed from water vapour by means of rentgen rays. in 1839 gay-lussac pointed to the great analogy between a gas and a dissolved substance. in 1870 rosenstich! made the following remarkable statement: ‘‘ the osmotic force is analo- gous to the elastic force of vapour.” use of thermodynamics —kirchoff applied thermodynamics (1858) to the vapour pressures of solutions, especially of sul- phuric acid. the law of mass action was deduced in 1864 by guldberg and waage, which they enunciated in 1867 in its present form: c (ab). c(de) = k-c(ae)- c(db), where c(ab) is the concentration of the salt ab, etc., and k isa constant dependent on the temperature (and the nature of the solvent). this formula holds good for a homogeneous equilib- rium, 7.e., one at which the four salts ab, etc., are totally dis- solved. fora heterogeneous equilibrium, at which somesalts, e.g., 138 ab, are not totally soluble, one has to introduce for c(ab) the concentration of the saturated solution of ab at the given tem- perature in the solvent used. guldberg and waage carried out a great number of experiments, especially on the cquilibrium be- tween the concurrent systems k»coq;+basq,4 and k.soy+ bacq;. they also made investigations on the velocity of reac- tions, especially of the solution of metals in acids. ‘they main- tained that the velocities of reaction at a given temperature are proportional to the concentration of the reacting substances, in this case the acid. the last equation therefore says that the quantity of aex db formed in a certain time is equal to the quantity of ab de transformed back to ae and db in the same time, in 1869 and 1873 horstmann deduced from thermodynamics the laws of chemical equilibria between gaseous substances. he found his conclusions verified by experiments. the theory of guldberg and waage was further simplified when horstmann showed that his formula (for gases) was applicable. latent heat—from the second law of thermodynamics, clapeyron had shown that the latent heat of vaporisation of water could be determined from measurements of the pressure of its saturated vapour at different temperatures, and, in 1860, utilised the formula of clapeyron for calculating the heat of vaporisation of ammonium chloride from the observed vapour pressure. from the known heat of formation of calcium car- bonate, horstmann (1870) calculated dissociation pressures which were verified by comparison with debray’s experimental values. similar calculations were made with regard to the pres- sure of water vapour over sodium phosphate dodecahvdrate. two years later guldberg took up the question of the evolution of carbon dioxide from calcium carbonate and deduced the famous formula: nn) where p is the dissociation pressure, t the absolute temperature, r the gas constant, a the inverse value (1-426) of the mechani- cal equivalent of heat, and g the heat of dissociation of 1 gramme; q is the corresponding value for 1 gramme-molecule when r= 2 (more accurately 1-985). equilibrium—tin 1885, van’t hoff showed that if a chemical equilibrium is expressed in the form a+b+c-+. . .x=k (e+ f+g+ ...y), k being the equilibrium constant, guldberg’s equation is applicable if k is introduced in place of p. disseciaiion.—i1n 1873 hortsmann continued his theoretical investigations on the question of <lissociation, using the experi- mental figures of wurtz on hydrobromide of amylene, csi1ibr, and those of wurtz and cahours on pentachloride of phosphorus, pci; . freezing points —in 1867, 1868 and 1870 guldberg demon- strated theoretically that the lowering of the freezing point of a solution under that of the solvent as well as the corresponding increase of its boiling point are proportional to each other and to the corresponding lowering of its vapour tension under that of the solvent. he gave the constants which represent the fac- tors of proportionality. ie verified his conclusions on the figures of wiillner and of riidorff concerning the behaviour of salt solutions in water. willard gibbs’ (1879) celebrated memoir on “ equilibrium of heterogeneous substances ”’ received little attention at the time of its publication. helmholtz (1882) independently developed part of gibbs’ deductions, more especially with regard to electromotive force. boiling points—raoult gave (1878 and 1882) important data regarding boiling points, vapour pressures and freezing points of solutions of a great number of substances in different solvents, whereas only aqueous solutions had been used pre- viously, the latter behave a little irregularly. he deduced em- pirical laws, the simplest of these, viz., physical chemistry where p= vapour pressure of pure solvent and p’= vapour pres- sure of a solution consisting of n molecules of solute in n mole- cules of solvent, was deduced subsequently by planck from theoretical considerations. from this formula the corresponding formula for the freezing point and the boiling point may be cal- culated according to guldberg’s deductions. it is supposed that the solute has no sensible vapour pressure, and that on freezing only the solvent separates out from the solution. electrolytic dissectation-—in 1877 tfeiffer measured the osmotic pressure of a solution of one gramme cane sugar in 99 grammes water at 6-8°c. and he drew van’t hoff’s attention to the measurement of pfeiffer. van’t hoff found that if the molecular weight of cane sugar is 342, and if it were possible to vaporise 1 gramme of sugar at 6-8° so that it filled 100 c.cm., it would exert a pressure of 508 mm. mercury according to avogadro’s law. the osmotic pressure is therefore within the errors of observation, and equal to the pressure the same quan- tity of matter would exert as a gas. this was of practical impor- tance in determining molecular weights. van’t hoff showed that two solutions of the same osmotic pressure possess common freezing point (or boiling point or vapour pressure), and proved his thesis by raoult’s experimental values. electromotive forces and chemical equilibria were attacked successfully, the vapour pressure p in guldberg’s equation being replaced by the equili- brium constant, k. , it was found that in the case of strong acids, strong bases and salts the molecular weight as determined by lowering of vapour pressures, lowering of freezing point, or rise in boiling point, was always less than the generally accepted value. this necessitated the use of an “ isotonic coefficient,” i, in the case of strong elec- trolytes. thus, for instance, potassium chloride in a solution of 03° possesses a molecular weight of only 39:2, 7.e. 1-9 times less than 74-5. his seemed very improbable. electric conductivity of solutions —in order to understand this, we must consider the electric conductivity of salt solutions. faraday found the first and fundamental law of this phenome- non. he observed that the quantity of metal deposited by a gal- vanic current on an electrode is proportional to the quantity of electricity which has passed through the electrode and also proportional to the equivalent weight of the metal. the first law is very natural; it was already enunciated but not strictly proved by berzelius. the second law, faraday’s law, says that equivalent quantities of different metals—and the same is true for other substances—are deposited on electrodes after the same quantity of electricity has passed through them. kohlrausch found that the molecular conductivity of a salt solution in water, 7.e., its specific conductivity divided by its concentration, increases with dilution. the ions of the salt carry the electricity with them according to faraday in equal quantity for each ion—we suppose, for simplicity, that the tons are univalent. now, in dilute solutions every ion travels inde- pendently of the other ions, and its mobility is dependent only on the viscosity of the solution which is caused by the friction against the solvent, in this case water. therefore, in highly diluted solutions every ion should contribute just as much as every other jon of the same kind to the transport of electricity— in other words, the conductivity should at a given temperature be strictly proportional to the number of ions, i.e., to the con- centration of the salt. since the conductivity increases at a slower rate than the concentration, the simplest explanation is to suppose that only some of the niolecules conduct, the others not tuking part. with increasing dilution, the non-conducting be- come conducting molecules. experience shows that the molecular conductivity, 7.¢., the specific conductivity divided by the molecular concentration, increases asymptotically to a maximum value for infinite dilu- tion, at which all molecules are conducting. if the molecular conductivity at a dilution vis called uw, and that at infinite dilu- tion is called p., the fraction of conducting molecules is evidently piu... this is of course true only at constant temperature and for rather dilute solutions, the fluidity of which may be regarded as equal to that of pure water. this fraction is called physical chemistry the coefficient of dissociation, because we must suppose that the non-conducting molecules have their generally accepted molecu- lar weight, just as other non-conductors according to van’t hoff’s law. on the other hand, the conducting molecules, e.g., of kcl, possess their conducting power only because their ions, the kation, in this case k, and the anion, cl, carry their atomic electrical charges (4-774 x10!" electrostatic units, posi- tive for each ion k and negative for each ion cl) in opposite directions through the solvent. it is evident that these “ mi- grating ” ions move freely until they mect an ion of opposite sign and unite with it, thus forming a non-conducting molecule, the total charge of which ts zero, and which therefore does not move along the potential gradient. in other words, we conclude that the conducting molecules are decomposed into their two ions and the degree of dissociation is measured by the fraction. dissociatian.—it is evident that a molecule dissociated into two free ions must exert double as great an influence on the lowering of the freezing point as a non-ionised molecule. if a molecule gives three ions, as for instance bacl., its action is three times greater after the dissociation than before it. gen- erally, if a molecule gives # ions its influence becomes # times greater in the dissociated than in the undissociated state. it is easy to sec that this circumstance gives a possibility of calcu- lating the degree of dissociation by means of determinations of the freezing point, or of the osmotic pressure of vapour pressure, or even of the boiling point of a solution according to raoult’'s laws. the solid basis of the theory of electrolytic dissociation is the good agreement between the degrees of dissociation calculated for dilute solutions from the electric conductivity and from the freezing point. electromotive ferce—in 1877 and 1882 welmholtz gave a thermodynamical theory of the electromotive force of galvanic cells which he confirmed by measurements, especially of con- centration clements. in 1888 and 188g nernst developed a theory of concentration elements founded on the theories of osmotic pressure and of electrolytic dissociation. it gave the same results as the theory of helmholtz for the total electro- motive force. but nernst went further. he calculated the three electromotive forces, at the junction between the two electrolytic solutions of different concentration and at the two contact surfaces between metal and electrolyte. in this latter case he expressed the potential diiference with aid of his con- ception of the ‘ solution pressure.”? planck gave in 1890 the theoretical formula for the more general phenomena of poten- tial differences at the contact surfaces between any two electro- lytic solutions. negbaur confirmed experimentally the theory of planck. the oxidation- and reduction-elements were also investigated from this theoretical view point by bancroit. transport or migration numbers of the ious.—uittori deter- mined the change of composition in different parts of a solu- tion contained in a long glass vessel, through which an electric current of given strength was carried during a measured tine in this manner he could calculate how much the positive and the negative ion each contributed to the conductivity. the cor- responding partial conductivitics are called the transport num- bers of the ions. if their sum is taken as unity, they are called migration numbers. the molecular conductivity of a solution 1s equal to the sum of the two transport numbers of the ions, multiplied by the degree of dissociation. ‘these numbers increase rapidly with, tempcrature, owing to the simultaneously diminishing frictional resistance to the motion of the ions. this resistance is regarde:] as chiefly due to the viscosity of the solvent. in water, the fluidity is nearly exactly proportional to the transport number of the acetate ion in the interval o° to 156°. the partial con- ductivities of the different ions approach to that of the acetate ion and to each other with rising temperature between o° and 306° according to experiments of a. a. noyes. theory of diffusion.—closely connected with his theory re- garding electromotive forces stands nernst’s theoretical calcula- tion of the diffusion coefficients for different electrolytes. here he ‘the change takes place. 139 supposed that the dissociation of the electrolytes was complete. his results agree fairly with experimental values found by differ- ent observers. the theoretical value is a little higher than the experimental one, which is easily explicable, as the dissociation is not complete and the osmotic pressure has not attained the limiting value. nernst’s formula indicates that hcl will diffuse more rapidly if a salt is added to its solution. this is easy to understand. if the if ion were alone in the solution, it would at 18° move 4-8 times more rapidly than if the cl ion were alone in the solution. but electrical forces cause them to move together, whereby the velocity of the diffusion diminishes to a mean value, 2-95. it is easy to show that the diffusion of if gn hci) increases with addition of sodium ions in good agreement with calculation (arrhenius, 1892). this is the most direct proof of electrolytic dissociations. additive propertics —if we dissolve a substance in water at a given temperature, we find that a certain property, c.g., the specific gravity, increases (or decreases) nearly proportionately to the percentage or concentration of the dissolved substance. tor sufficiently dilute solutions the proportionality is exact. if the dissolved substance is dissociated, the property p may be expressed as the sum of three terms, the first one the property p,.of the solvent, mostly water, and the two others proportional to the concentration of the dissociated parts, mostly ions. in other words, the following equation holds: pi srp + lgc: + acg; tf there are only two ions / and / the two terms ayc; and ac; sullice. ay and keare two conslants, characteristic for the ions £ and j. if we now dissolve another substance, e.g., a salt, which dissociates into the ions j and l, we have pi = or dery: “nc, consequently; | p;; = py = kc; == a3c) if we now choose the concentration, ¢c.¢., expressed in molarity equal ton p3; — pi, = n(a» = k3) in other words, the difference between the properties of two salts with a common ion j is proportional to the concentration and to the difference between two constants ae and ay charac- teristic for the two ions j and l; they may be accompanied by any jon i of the opposite electric charge. this is the law of adiitive properties, which is only valid for totally dissociated salts, z.¢., at extreme dilution. but it is found that also for higher concentrations this law is often valid. this depends upon the circumstance that in many cases the eflect of the undisso- ciated part is very nearly equal to the sum of the etfects of the ions contained in it. this peculiarity 1s often explained so that the salt is completely dissociated. but in some cases, e.g., for the lowering of the freezing point, it is found (by raoult) that the property is net additive, which depends upon an incomplete dissociation. ‘thermociemistry during chemical changes heat is usually evolved or absorbed, the amount depending generally on the temperature at which many measurements were made by berthelot and julius thomsen in the latter part of the roth century. before the introduction of the calorimetric borab = (con- stant volume method) determinations of the heat evolved or alsorbed were usually carricd out at constant pressure. since change in volume generally occurs, the results obtained need correction in order to obtain the theoretically more important value, the heat of reaction at constant volume. for if a reaction takes place at constant pressure p and the volume v at the end of the reaction is less than vo the initial volume of the reacting substances, the amount of work p(v—vo) done by the system 140 on the surroundings has a negative value, i.e., this amount of work has been done on the system and the heat of reaction is correspondingly greater than if the reaction had taken place at constant volume. frequently, the heat of a reaction a is incapable of direct measurement. usually it is possible to carry out two (or more) partial reactions b and c whose algebraic sum is equal to a. for the heat changes u,, u,, u. we have the equation ue = lo +u,. so that two of the quantities being known from experiment we obtain the third by addition. berthelot and thomsen believed that the direction of a reac- tion depends on u being a positive magnitude, #.e., heat being evolved. reactions in which heat is evolved are called exother- mic, those in which it is absorbed, endothermic. berthelot tried to explain the occurrence of endothermic processes by main- taining that foreign (not caloric), ¢.g., electrical energies, inter- fered in the process. now we know that the free energy, usually denoted by a, is the determining quantity, and thereby the values of u have lost a great part of their importance. it is to be observed that at absolute zero u=a, and that at low tem- peratures the difference u—a is rather small compared with u in most cases, therefore the mistake of the thermochemists is explicable. the values of u and a may easily be calculated if we know how u changes with temperature. according to a theorctical formula of debye the specific heat is proportional to the third power of the absolute temperature in the neighbourhood of absolute zero. with the knowledge of the specific heats of the reacting substances at higher temperatures it is pos- sible to find the value of u at any temperature with sufficient approximation, if this value is known at ordinary temperature. at t=o0, u=a. as according to the second law of thermo- dynamics, tda = (a—u)dt, it is possible to find a at any temperature, when u and da—dt are known, as nernst describes in his treatise on “‘ the new heat-theorem.” the free energy .\ corresponds to the potential energy in mechanics, and therefore any chemical reaction will proceed in such a direction that a decreases. jn certain cases a can be measured directly, as with galvanic cells. chemical equilibria.-—the simplest case of an equilibrium is that between a liquid and its vapour, discussed above. the same formula is valid for the solubility of a substance in a solvent, and also for the equilibrium-constant, characteristic of a chemi- cal reaction. the simplest chemical reaction is that of the un- dissociated part of an electrolyte with its ions. this equilibrium has been investigated by ostwald fcr weak acids and by bredig for weak bases, and it has been found valid (ostwald’s law). by means of the change of the equilibrium constant of weak acids arrhenius calculated their heat of dissociation and from this their heat of neutralisation in good accordance with thermo- chemical observations. the equilibrium constant of dissociation in all cases investigated at not too low temperatures diminishes with increasing temperature, whereby the heat of dissociation is found to be negative at higher temperatures. therefore some weak acids possess a lower conductivity at higher than at lower temperatures, which was previously regarded as impossible. the calculations agree very well with the observations. the phase rule-—for heterogeneous equilibria, gibbs has given hisimportant phase rule. we may at first regard the simple case of water. water occurs in three different modifications, as ice, water and vapour. for each of these is valid an equation of condition f(p,t,c} = 0, where p and t represent the obtain- ing pressure and temperature and c is the concentration of the substance in the ice phase, liquid phase and vapour phase. if the three phases co-exist in a vessel, we have three equations for determining the three variables. from the tables of vapour pressure at different temperatures we find p=4-57 mm. hg, t = 00076°c. the three concentrations are proportional to the densities. here we have only to do with one substance. the number of phases is threc. if we had put a sufficient quantity physical chemistry of a soluble salt, e.g., sodium chloride, in the water, two solid phases—one of ice, another of salt crystals, one fluid—salt solu- tion, and one gaseous—water vapour would have been present. these can only co-exist at the eutectic point, —21-3°. in gen- eral, if we have 2 substances they may give #-+2 phases at the “point of transition.”” if we take away one phase, e.g., the solid in the first example, we have only two phases, vapour and fluid, above the transition point. then we may fix one of the variables p or t, but then the other becomes determined, e.g., p as a func- tion of temperature. if also another phase, e.g., the gaseous one, disappears, we may choose any pressure and temperature, but if these are fixed, we obtain also a fixed concentration, which in this case may be expressed in gramme water per cubic centi- metre. the phase rule owes much to roozeboom and schreine- makers, and van’t hoff has applied it in his remarkable investigations on “ oceanic deposits of salts.” an interesting equilibrium is that which occurs when an acid is added to a solution of a salt of another acid. in this case a certain quantity of the corresponding salt of the first acid is formed. julius thomsen and ostwald determined this decom. position by thermal and optical measurements. arrhenius found very good agreement of these values with those calculated from dissociation constants. adsorption phenomena.—if we have a substance, e.g., acetic acid, dissolved in water containing charcoal particles i in suspen- sion, we find that a great deal of the acid is “‘ adsorbed ” by the particles so that after some time equilibrium is attained, at which point, according to freundlich, = kc, where y is the adsorbed quantity per gramme of charcoal, k is a constant dependent on the origin and history of the charcoal and the temperature, c is the concentration of the acid remaining in the aqueous solution, and n a constant number. this equation has been verified in a great number of cases, though the theo- retical deduction is lacking. at os values of c, n diminishes with increasing c. the adsorption phenomena play a very great role in colloidal chemistry, and therefore also in biochemistry. (see collorps and biochemistry.) amphoteric electrolytes which have both basic and acid char- acter play an important rele in biochemistry; their equilibria have been investigated by many biochemists, especially by jacques loeb. velocity of reactions —the rate of change of a chemical pro- cess is proportional to the concentration of the catalyst (q.v.) and that of the substrate. sometimes the quantity of the cata- lyst changes also during the chemical change. in this case the change of its concentration must be taken into consideration. of this kind are the so-called autocatalytic processes. the agree- ment of theory with experiment is satisfactory. the effect of the catalyst in most cases ii or oh!’ ions is affected by the presence of neutral salts, the so-called salt-action. in most cases their action accelerates the velocity; in some cases, ¢.g., saponification of esters, the velocity diminishes when salts (of the type kcl) are present. arrhenius found that the same equation is valid for the in- crease of the velocity of reaction with temperature as that for the corresponding change of the constant of equilibrium. this equation has proved to be generally valid. he therefore sup- posed that only a very small part of the substrate reacts chemi- cally which is in chemical equilibrium with the chief, very nearly total, quantity of thesubstrate. the “active” part of the substrate may be an allotropic form of the chief part, or it may consist of the molecules which have a very great molecular motion (marcellin). trautz, mcc. lewis and perrin inde- pendently of each other expressed the idea that the radiation of heat provokes the formation of the active substrate, and that a special radiation, in most cases infra-red and different in different cases, activates the molecules. it is difficult to give experi- mental proof of this theory. the ‘ heat of activation ” q in the formula is very different physical training in different cases. for the reactions investigated, saponifications of ethyl acetate and inversion of cane sugar by acids, q has the values 5,579 and 12,800, which are of the same order of magnitude as that of q for common chemical processes. for biochemical processes we find very different values, from q=3,150 for the precipitation of egg-white, and q=5,oc0 for the inversion of cane sugar by means of invertase, up to q= 81,000 for the spon- taneous destruction of tetanolysin and q=9g9,200 for that of a haemolysin from goat-blood. the spontaneous <lecomposition of the raclioactive substances does not change within the very widest limits of temperature. the same is the case for some photo-chemical processes such as the common photographic process with silver bromide and gelatine, or the reaction of oxalic acid with ferric chloride. in other cases the temperature has a comparatively small influence (o is sometimes about 2,000) on photochemical processes. activity—the determination of dissociation constants by different methods, e.g. electric conductivity, electromotive force of concentration cells, lowering of freezing point, etc., only gives concordant results in the case of dilute solutions. for con- centrated solutions clisagreement results from the circumstance that the conductivity depends upon the molar concentration, whereas the thermodynamic phenomena are connected with the numerical concentration. but even in rather dilute solu- tions, below o-1 normal, for which the two kinds of concentration are very nearly proportional, very great discrepancies are observed. this depends on the corrections which should be applied in different cases. milner showed that a correction ought to be introduced for the thermodynamic quantities, espe- cially the value of the molecular lowering of the freezing point. debye and hiickel found that another correction should be applied to the determinations of molecular conductivity. these two corrections are due to the influence exerted by the electrical charges of the ions. other corrections ate due to the viscosity, which has a great influence on the conductivity but probably none or only a very small one on the freezing point. in great dilutions this correction vanishes. but this is not the case with that due to the hydration of the ions, which has an opposite influence on the conductivity to that on the freezing point. even the change of the dielectric constant may have some influence. these different corrections are still only imperfectly investigated. in order to escape all these difficulties, many authors as milner, debye, and hiickel, accepted an idea of sutherland, that the strong electrolytes are completely dissociated, or they may practically be regarded as completely dissociated (bjerrum). it is also maintained that even crystals are completely disso- ciated, because their r6ntgen-spectra are caused by atoms and not by molecules, that therefore we must suppose that also the most concentrated solutions of strong electrolytes are com- pletely dissociated. it is difficult to understand this, for ions are free to move under the influence of electrical forces, and that is very rarely the case with the atoms of a crystal. it is true that such a migration is found for sodium atoms in quartz crystals, but they must be regarded as being in solid solutions together with sio’’s-ions in the crystal. glasses are also electrolytes, but are regarded as extremely viscous fluids. the change of the molecular freezing point and of other con- nected properties with concentration is explained as depending on a property called activity, which is empirically determined, but so that the thermodynamical laws shall be valid. the inves- tigations regarding activity have increased our knowledge, but a theoretical explanation of the physical causes for the complicated change of the activity with concentration has not been given. see atom; biochemistry; catalysts; colloids; crystallo- graphy; electron; isotopes; matter; physiology; etc. the chief english textbooks are: s. arrhenius, textbook of elec- trochemisiry (1902); sir james walker, introduction te physical chemistry, 9th ed. (1922); w. nernst, theoretical chemistry (1923); a.: j. allmand and h, j. t. ellingham, applied electrochemistry (1924); j. r. partington, chemical thermodynamics (1924); h. s. taylor, ed., physical chemistry (1924); m. de k. thompson, the- oretical and applied electrochemistry (1925); w. mcc. lewis, a system of physical chemistry (1925). (sv. a.) i4i physical training.—the history of physical training since rgio has been marked by (1) a notable improvement in the whole basis of the training itself, (2) a growing recognition of the value of such training during the formative years of child- hood, and (3) the growth of administrative measures directed toward the establishment of a uniform system of training in all the schools which form part of the national system of education. i. in great britain until 1902, physical training was permissive in the elementary schools; in that year it was established as an integral part of the curriculum, and the board of education issued a model course for the upper departments of the schools. under successive revisions the model course, which originally consisted largely of military drill, has developed into the present syllabus of phy- sical training, based on the swedish system and providing for the needs of all children between the ages of 5 and 14. faith in the sufficiency of mechanical drills has been succeeded by a broad conception of physical education as a many-sided and vital process, directed to securing the careful and well-balanced cultivation of the physical powers of each individual child, and to the formation of habits of self-discipline by learning to con- trol the body and to work in harmonious concert with others. physical education as now understood includes systematic and graded exercises chosen for their physiological and corrective results, folk-dancing, swimming, organised games and sports, in fact all those things which make for physical well-being, im- plant a love of healthy outdoor pursuits, and contribute to the making of useful citizens. in 1909, the medical department of the board of education was made responsible for the inspection of physical training in all state-aided schools and institutions and for the general super- vision of the arrangements made for such training by the local education authorities. in all the elementary training colleges physical training as a professional subject was made compulsory, and encouragement was given for the formation of courses for the teachers already in the schools. a special grant was estab- lished in 1917 for the purpose of encouraging local education authorities to employ expert organisers of physical training, who should assist the teachers by advice, demonstration and training to make the most of their opportunities. the results obtained have abundantly justified the policy of the grant, and have shown that the organiser is an essential factor in a scheme of training under which the class teacher is responsible for the instruction of his own class. the physical training in the ele- mentary schools has thus been directed into the right paths and the efficiency of the teaching steadily improved. the varied problems connected with the physical training of adolescent girls and boys are not capable of solution on the basis of a common syllabus for secondary schools. reliance therefore has to be placed on the trained teacher who can formulate and carry out his own schemes. girls’ secondary schools can gen- erally obtain the services of an expert teacher trained at one of the several physical training colleges for women. for this reason the physical training at the girls’ schools, at least in the better ones, has for some time been conducted on the right lines. training in secondary schools.—much less progress has been made with the boys’ secondary schools, due partly to the lack of properly trained men teachers and partly to the fact that the need for systematic training has not been so fully recognised. the tendency has been to regard games as sufficient for the boys’ physical development. it must, however, be admitted that the physical training of which these schools have had ex- perience has not inspired general confidence in the efficacy of this form of instruction. recent experiments indicate that a specialist training in physical education is unlikely to attract men of the right type in sufficient numbers to make the institu- tion of a prolonged course of training an economically sound prop- osition. a solution may be found in encouraging the ordinary form masters to take part in the work after undergoing a short course of training, and in providing some instruction for students in secondary training colleges. 142 secondary schools generally have facilities for physical train- ing which the elementary schools do not possess; they have their own playing fields and usually some form of indoor accommoda- tion, often a gymnasium, the classes are smaller and suitable clothing is worn. but in many of the secondary schools the growing pressure of whose academic work is often allowed to crowd physical training out of the time-table of the older pupils, the advantage of systematic physical training throughout the whole of school life needs to be more fully recognised. (sce education: literature.) (f. h. g.) il. in the united states physical education advanced with giant strides in the united states during the years 1910-26. the world war had a powerful influence in centring attention on this subject, because one out of every three who were examined for service was rejected on account of disability. before 1915, only three states had laws requiring the teaching of physical education in the public schools. during the period of the world war and the three years follow- ing, 25 states passed acts compelling the teaching of physical education, and between 1921 and 1925 six other states passed similar laws, bringing the total to 34. most state laws provide for the organisation and supervision of courses in physical education for both sexes in the elementary, secondary and normal schools. many states have made pro- vision for training teachers in this subject in the normal schools, the courses for which must be passed satisfactorily before can- didates are given their licence to teach. the professional training of teachers has contributed greatly to the advancement of physical education. there were in 1925 more than 40 schools, including normal schools, colleges, universities and private schools which graduate well-trained teachers, and the number is rapidly increasing. about 95% of the preparatory schools, colleges and universities have departments of physical training. several states have a state director of physical education with assistants to supervise the work. it also has become the practice in large cities to have directors. the time requirements for exercise for the pupils average from 15 to 30 min. daily. it is estimated that the total cost of physical education in the public schools of the united states was in 1925 more than $ 5,000,000. systems of training —the german and the swedish systems made definite contributions to the cause of physical education, but their formal work found their strongest opponent in the british system of playing games, which gradually has become the dominating principle of physical education in the united states. marching, dancing, free-hand exercises and calisthenics with dumbbells or wands, usually form a part of the formal drills, but emphasis is laid upon the exercises in which play is the central theme. no nation in the world has so many outside agencies organised to promote the spirit of play either as a means of physical education or in conjunction with its main purpose. foremost among these is the playground and recreation assn. of america, which is aggressive in arousing public interest in favour of play spaces with instructors, especially for the children. as a result of the momentum given, in part by this association, more than $20,000,000 are now expended annually in the united states for public recreation. many thousand paid and voluntary workers give instruction in organised play in over 8,000 playgrounds and gymna- siums, several other national organisations, working independently, practically all being constituent members of the national amateur athletic federation, are promoting and administering programmes of physical education, some of them of a high order. among these should be mentioned the y.m.c.a., the ¥y.w.c.a., american turner bund, american legion, bohemian sokol, the national assn. of state high schools, boys’ club federation, catholic boys’ brigade, boy scouts of america, girl scouts, camp fire girls, jewish welfare board, order of demolay, the national collegiate athletic assn., the amateur athletic union and the knights of columbus. other organisations not now nationally organised, such as municipal recreation depts., athletic clubs, industrial companies, settlement houses, churches and sunday schools, civic and fraternal organisations, etc., also are doing valuable work in physical education. it is estimated that more than 10,000,000 boys of elemen- tarv and high school age receive physical training from the above and other organisations mainly in athletic games. (a. a. st.) physics physics.— while recognising the tendency of each generation to consider itself important and its contributions to progress unique, the historian of the future will probably estimate the 30 years ending with 1925 as the most extraordinary in the history of the world up to the present in the number and the fundamental character of the discoveries in physics to which they have given birth, and in the changes brought about by these discoveries in man’s conceptions as to the nature of the physical world in which he lives, there has been no period at all comparable with this unless it be the period about 300 years ago, which saw the development of galilean and newtonian mechanics. ‘this was indeed of in- calculable importance for the destinies of the race. the con- ceptions then introduced are not only the basis of modern mute- rial civilisation, but they were the cause of a very complete change in man’s whole intellectual and spiritual outlook—in his philosophy, his religion and his morals. but the discoveries in physics of the past 30 years justify the expectation, at least, of as great if not greater consequences—consequences, too, which are already beginning to be realised. to appreciate how stupendous a change these discoveries have already wrought in human thought, it is only necessary to reflect that of the six basic principles which at the end of the roth cen- tury acted as the police oflicers to keep the physical world run- ning in orderly fashion, namely, the principle of the conservation of the chemical elements, the principle of the conservation of mass, the principle of the conservation of energy, the principle of the conservation of momentum, the principle underlying maxwell’s electrodynamics, the principle of entropy or the second law of thermodynamics, kia tal there is not one, the wiversal validity of which has not been questioned recently by competent physicists, while most of them have been definitely proved to be subject to exception. the principle of the conservation of the chemical elements went with the discovery of radioactivity. the principle of the conservation of mass vanished with the experimental discovery of the increase in the mass of the electron with speed as the velocity of light is approached. ‘the principle of the conserva- tion of energy suffered a change in aspect when both experi- mental and theoretical evidence came forward that energy and mass are related by the einstein equation mc?= fe, for tn that equation the ideas of energy and of mass become complctely scrambled. the principle of the conservation of momentum is denied wziversality by the quantum theory. the maxwell equa- tions are violated in atomic mechanics. the principle of entropy is thus far the only entirely unimpaired rudder to the ship of rgth-century thinking. further the speed with which new discoveries and new points of view are coming into modern physics shows as yet no abate- ment. fifteen years ago it was thought that the revolution had pretty well spent its force, that the main group of new ideas had already been introduced. but a listing of the most outstanding discoveries of the past 30 years shows that the great majority of them belong exclusively to the period here in review—namely, the last 15 years—and all of them belong at least in part to this period. the immensity of the progress made within it will be best appreciated through a rapid review of this whole list and brief comments upon the origin and the particular significance of each discovery. 1. the discovery of the electron this was a very gradual process covering about 150 years and participated in by many workers. franklin, faraday, weber, helmholtz, stoney, lor- entz, zeeman, j. j. thomson, lenard, townsend, wilson and others,! but the actual isolation and the exact measurement of the electron occupied the first seven years of the period in review,? 1910-25. 2. the discovery of x-rays—this falls clearly outside the present period but practically the whole of the quantitative work- ing out of the properties of x-rays and the great discovery in 1912 of their wave nature’ lies wholly within it. physics 3. the discovery of ouantum mechanics——this began at about the year 1900 with the work of planck, but the last 15 years have contributed enormously to it, as will appear as the enumeration of discoveries proceeds. 4. lhe discovery of the principle of relativity--though the special principle dates from about 1905 and therefore lies within the first half of the last 30-year period, the formulation by ein- stein of the general principle belongs wholly to the period in review. its birthday was in 1915 and its most precise and sig- nificant experimental verification through the measurement of the bending of starlight in going past the rim of the sun, the dis- covery of the enormous spectral shift of lines coming from the companion of sirius,t and the beautifully consistent measure- ments of the displacements of solar spectrallines,’ has all been the work of the past few years. it is too early to estimate the sig- nificance of d.c. miller’s very recent observations on ether-driit. 5. the discovery of radioactivity—this belongs indeed wholly to the first half of the 30-year period, but the definite proof that lead is a product of the radioactive disintegration of both uranium and thorium, and the application of this fact to the fixing of the minimum age of certain uraninites from the black hills in south dakota as 1,677,000 years,® to take but a single concrete case, is very new and marks an important ad- vance in the process of elaborating a very much more definite geologic time scale than has heretofore been available. 6. the discovery of the nuclear atom, through the experiments on x-ray scattering begun about rgr2 and carried on for 10 years, mostly at manchester and at cambridge, england,’ fails wholly within the last 15-year period and has been epoch-making in its consequences. 7. the discovery of crystal structures, through the aid of x-ray spectroscopy® dates from only 1913. it has completely revolutionised crystallography and opened up a new world of definite knowledge about molecular and atomic arrangements in solids. 8. lhe discovery of atomic numbers (1913-24) and the def- nite fixing of the total number of possible elements between hydrogen and uranium as g2,° both being included, is perhaps the most beautiful and the most simplifying discovery ever made. nature never came so near surrendering herself to her lover without reserve and revealing herself in beautiful and simple grandeur as when moseley found that all the elements fitted into a single arithmetical progression—a progression, too, which could mean nothing except that the positive charge on the nucleus of each atom moved up by unit steps from 1 to g2 in going from hydrogen to uranium—a progression which at once robbed atomic weights of their long-usurped right to act as arbiters of the chemical destinies of atoms, and restored this place to its legitimate possessor, the electrical charge of the nucleus. some day a poet will arise who will make an epic for the ages out of young moseley’s discovery. the x-ray spectroscopists'!® and those who have recently extended the x-ray laws into the field of optics, have contributed to the establishment of the com- plete generality of the moseley progression, but they have merely finished the structure which he designed. 9. lhe discovery that the energy communicated to electrons by ether waves is proportional to the frequency of the absorbed waves.—this was vaguely suggested by planck in 1900, more specifically by einstein in 1905, but the experimental proof of its correctness is perhaps the most momentous achievement of modern physics, and it has all come about since 1912. ‘the achievement is momentous not merely because the equation 3 mv?=h.—p ranks with the equations of maxwell in its conse- quences, but because the relation itself is new, undreamed of in 1895, and altogether revolutionary, demanding a return to some elements of the corpuscular theory of ether waves. it was proved first very exactly in photoelectric experiments with light waves, then during and after the war with x-rays," and then with y-rays.4 most of the preceding discoveries were wonderful additions to knowledge, explorations in heretofore unknown fields but not subversive o: established conceptions. ‘this one, however, wrought havoc with existing theories and demanded a 143 new formulation of ideas about the relations of ether physics and matter physics. its significance for the future can scarcely be overstated. 10. the discovery of the meaning of spectral lines-——bohr“ in setting up his theory of atomic structure merely gencralised the preceding discovery. with unusual insight into the method of constructive science, he incorporated all the past and merely superposed upon celestial mechanics the assumption, almost inevitable gif einsiein’s equation is correct) that when an ether wave is emitted as well as when it is being absorbed the foregoing relation between energy and frequency still holds, z.e., that the emitted wave frequency is given by e.—e,=h,, the ef, and e,; being the electronic energy before and after emission. combining this with the experimentally established ritz-balmer equation, he brought out sharply the unitary or atomic character of angular momentum, clearly one of the two or three most fundamental discoveries of all time, for it will presumably always be the basis of all atomic mechanics. it had been dimly glimpsed before in the work of planck and einstein, definitely stated by nichol- son and ehrenfest, but from bohr’s time on quantum theory took on a definitertess, almost a visualisability before unknown. 1. the discovery of isotopes —this discovery did not begin to be made until 1913, when chemists and physicists approached it from two different angles; first, the chemistry of the radio- active elements and second, positive ray analysis.“ it was com- pleted only after ro years of work by physicists in analysing by positive ray methods 46 of the first 55 elements of the periodic table. its significance lies in the four following facts: first, that it has resurrected completely the discredited and amazingly simple prout hypothesis that the masses of all atoms are exact multiples of the mass of a primordial atom; second, that it has enabled us to count with certainty the exact number of positive and negative electrons inside every nucleus—positives being equal in number to the atomic weight, negatives to the atomic weight minus the atomic number; third, that the failure of hydro- gen to fit exactly into the above scheme constitutes excellent evidence for the einstein conclusion as to the interconvertibility of mass and energy; and fourth, that the difference in stability (decay-time) of radioactive isotopes suggests new possibilities in the reading of the structure of the nucleus, 7.c., it gives us new eyes for peering inside the tiniest organism yet found—the nucleus of the atom. 12. phe discovery of “ the excited atom.”—the purely theoretical reflections in 1921 of two mere youths in denmark, klein and rosseland, resulting in the proof that if atoms can be thrown by impact, as experiment shows that they can, into a quantum state of higher energy than the normal—appropriately called an excited state—then unless the second law of thermo- dynamics is to be violated there must be a heretofore unrecog- nised mechanism by which an excited atom can return to its normal state without radiating at all, but rather by throwing back all the potential energy of its excited condition through a so-called “ collision of the second kind ” into an electron or an atom projected from the collision with a kinetic energy that may be roo times the average energy of molecular agitation. this is a very recent discovery of the first magnitude and of possibly immeasurable significance. it has already made it possible through the work of the experimental physicist!* to see a collision- mechanism by which a negligible number of mercury atoms can absorb ether-wave radiations and transfer that energy to the act of exciling thallium atoms to radiate their characteristic frequencies. it for the first time reveals a definite mechanism, sought in vain by the best thinkers of the roth century, by which the energy of ether waves may be absorbed by matter and trans- formed into heat. it takes in one case, at least, the mystery out of the words “ catalytic agent.” it suggests why very minute quantilics of vilamines, etc., may be the intermediaries through which very vital processes are brought about. it makes the future bright with promise for the better understanding of explo- sive processes. indeed the properties of excited atoms may pos- sibly be the foundations of a new era in both industrial and biological science. 144 13. the discovery of the artificial disintegrability of atoms.— this was glimpsed about 1912 through the appearance of hydro- gen lines where hydrogen unless artificially produced from other elements should not have been present, and new claims of spec- troscopic evidence of a similar sort are now being advanced, but the unambiguous proof is contained in rutherford’s !? direct experiments showing that hydrogen atoms can be knocked out of other atoms by alpha-ray bombardment. the method shares with that which will introduce new resolution into the study of the masses of isotopes, the promise for the future reading of the _ conditions of the electrons within the nucleus. 14. the discovery of relativity inside the atom—it was as late as 1917 before sommerfeld'® began his wonderful work on the interpretation of the fine structure of spectral lines—work which began for the first time to reveal the correct principles underlying quantisation, finally so penetratingly formulated by epstein. seldom in the history of physics have purely theoretical formulae had such amazing successes in the field of precise pre- diction as have sommerfeld’s relativity-doublet formulae and epstein’s extension of the same sort of orbit considerations to the prediction of the number and character of the multiplicity of lines found in the stark effect. the whole interpretation of spectroscopic line structure through changes in so-called azi- muthal and inner quantum numbers is one of the great achieve- ments of all time resulting from the interplay between pene- trating theoretical analyses and skilful and refined experimental technique. ts. the discovery of new experimental techniques for see- ing invisible ether waves—such long-wave technique’? has completely bridged within the past two years the gap between artificial electromagnetic waves and heat waves, and in the short- wave region hot-spark vacuum spectrometry”? and beta-ray methods of analysis have practically filled in completely the gap between the optical and the x-ray fields, while far above even the gamma rays of radium a new group of rays of well-nigh infinitely high frequency has been found (see below). this con- tinuous passage of frequencies from a thousand billion billion per second, over into the zero frequency, 7.e., over into static electrical fields, all these waves possessing identical character- istics as to speed of propagation, as to polarisation and as to relations of electric and magnetic vectors, demands one and the same sort of transmitting mechanism or medium to take care of them all, by whatever name it may be called, whether a “ world- ether ” or ‘‘ space,’’ this last term meaning no longer emptiness, but emptiness endowed with definite properties, if such an hibernicism suits one’s taste. 16. the discovery of new properties in conduction electrons, —the direct measurement” of the mass of conduction electrons, the discovery of a general increase in conductivity with the application of enormous pressures,”* of superconductivitiestm and the very recent proof that, when intense electric fields pull con- duction electrons out of metals, the energy of thermal agitation assists not at all at ordinary temperatures but does assist at very high temperatures,” all these recent discoveries, especially the last, begin to clear up the contradictions in the electron theory of metallic conduction, and to enable the quantum theory of specific heats to be applied in a new and illuminating way to the condition of the electrons in metals. the new results are full of promise for the better understanding in the near future of the moot subject of metallic conduction. 17. the discovery of quantum jumps inside the nucleus.— the very recent proof?® that gamma radiations obey the same quantum jump laws obeyed by x-rays and light rays and the still more recent proof that the initial act in a radioactive change is the ejection of an alpha or beta ray—possibly by virtue of the actual loss of mass of the nucleus through electronic settling and the transformation of this mass into the energy of the ray, follow- ing the einstein relation governing the interconvertibility of mass and energy—this is a discovery of the first importance for the future understanding of one of the most fundamental pro- cesses in nature, namely the growth and transmutation of the elements. physics 18. the discovery thai the law of the conservation of momen- ium is applicable to the encounter between a light quant and a free electron—this very recent and very amazing discovery ?? seems to put the final nail into the einstein conception of radiant energy travelling through space in the form of vibratory light darts of some sort, but at the same time it emphasises the appar- ent impossibility of the physicist finding in his present stage of development any one consistent and universally applicable scheme of interpretation. it is a discovery of the very first magnitude, one of whose chief values may be to keep the physi- cist modest and undogmatic, still willing, unlike some scientists and many philosophers, not to take himself too seriously and to recognise that he does not yet know much about ultimate realities. 19. the discovery of the summation of two quantum jumps into a single monochromatic ether wave-—vthe very recent proof brought forth first by the properties of band spectra?? and second by the discovery of two electron jumps through study of pp groups in line spectra,?® that an atom can integrate the combined energy of two distinct and simultaneous quantum jumps into a single emitted monochromatic wave,is of funda- mental importance, because of the new light which it throws upon the nature of the act in which a ray of light is born and pro- jected on its way through space. the discovery of two electron jumps uniting into a single monochromatic ether wave seems to preclude the possibility that there is any vibrating mechanism in the atom executing vibrations synchronously with the period of the emitted monochromatic wave. that the atom has this power of transforming, in some as yet mysterious way, the energy of every atomic shudder into a monochromatic ether wave is amazing. whether we shall ever be able to visualise the process more definitely than we can now no one knows. 20. the discovery of the failure of the relativity explanation of all relaltivity-doublets—the impasse pointed out within a year °° between the heretofore recognised causes of doublets in optics and in x-rays, an impasse which necessitated the finding of a new cause which would yield exactly the same formula as the relativity cause—a really terrible necessity in view of the extraordinary quantitative success of the purely theoretical formula following from the mere postulation of the change of the mass of the electron with speed—this impasse has apparently just been resolved within two months by two young dutchmen, oulenbech and goudsmit, who find, mirabile dictu, that the assumption that every electron in the universe spins with one unit of angular momentum either right-handedly or left-handedly yields a formula of exactly the same form as does the relativity cause. this assumption not only saves the relativity explanation but, combined with it, furnishes a much better correlation of all present spectroscopic facts than we have heretofore had. it represents probably a fundamental advance in our understanding of the nature of the most nearly ullimate thing with which physics deals, namely, the electron. the physics of the future bids fair to hear much of the spinning electron. (21) the discovery of cosmic rays."—that something very fundamental is going on all through space, that nuclear trans- formations each of enormous energy value corresponding to the fall of an electron through as much as 30,000,000 volts, are actu- ally taking place in all directions about us in the outer stretches of the universe and that the signals of these cosmic changes can be detected here has just been proved. it is a discovery most stimulating to the imagination. call it the music of the spheres if you wish! anyway man can hear it now and may sometime know more about it. of these 21 fundamental discoveries, at least 16 fall wholly within the past 15-year period and all of them have belonged in no small degree to it. physics as yet seems to show no signs of approaching senility. what the future has in store, no man knows but at present there seems to be well-nigh limitless possi- bilities ahead for applications even if the pace of discovery should sometime slacken. references.—1. the electron, chap. i-iii. (univ. of chicago press, 1924). 2. millikan, phil, mag. (july 1917); see also the electron. 3. von laue, friederich and knipping, sitz. ber. d. physiology miinchener akad (1912); also jahrbuch ftir radioaktivitat u. elek- tronik, il., 308 (1914). 4. walter a. adams, aff*, wilson obseria- tory contributions (1925). 5. charles e. st. john, mt. wilson ob- servatory contributions (1925). 6. c. w. davis, amer. jour. science (march 1926). 7. rutherford, geiger, marsden and chadwick, phil. mag., 21, 699 (1911); 25, 604 (1913); 40, 734 (1920); 42, 933 (1922). 8 bragg, vy-rays and crystal. structure (bell, london, 1916). see also ewald, aristaile un. rontgenstrahlen (springer, berlin, 1923). 9. moseley, phil. afag., 26, 1024 (1913); 27, 703 (1914). 10. siegbahn, spektroskopie der renigenstrahlen (springer, berlin, 1923). ir. millikan and bowen, physical review (1925). 12. the hiectron, chap. 10. 13. duane, physical review, 7, 599 (1916); 9, 568 (1916); 10, 93 and 624 (1917); de broglie, third selvzay con- gress (1921); 14. ellis, proc. roy. soc., 99, 261 (1921); alsosame jan. 1924. 15. n. bohr, phil. alag., 26, 1, 476, 857 (1913); see also the electron, chap. 9. 16. sce ashton’s isotopes (london, 1922). 17. see loria, phys. rev., nov. 1925, and proc. nat. acad., dec. 1925, for review of experimental work of franck caria, donat and loria. 18. rutherford and pupils, phil. afag. (1920-5). 19. sommerfeld, ““atombau u. spectrallinien,” vieweg uw. soku, braunschweig, chap. 6 (1924). 20. nichols and tear, phys. rev. (1925). 21. millikan, astro. phys, jour. for i920and millikan and bowen, phys. rev. (1923 and 1925). 22. r.c. tolman, phys. rev. (1920-3). 23. bridgman, phys, rev. (1925). 24. kammerlingh onnes, contributions from the univ. of leiden (1910-5); 25. millikan and eyring, phys. rev. (jan. 1926), 26. ellis and rutherford, proc. roy. soc. (1925 and 1926); meitner, zeit. f. phys. (1925). 27. a. h. compton, piys. rev. (1923, 1924 and 1925). 28. sommerfeld, ‘“ atombau, etc,” chap. 9. 29. russel and saunders, a sero-phys. jour., 1925; wentzel, zeit. f. phys. (1925); bowen and millikan, phys. rev. (1925). 30. millikan and bowen, phil. afag. (1925). 31. high frequency cosmic rays, phys, rev. (may, june and sept 1926). (see also astronomy; atom; atomic energy; atomic weigiits; cilemistry; crystallograpity; electricity, conduction of; erier; gases, electrical properties of; jsoropess: matter; qvantum theory; raproactrtvity; rays; relattiviry; solar energy; space-time; spectrum; transmutation of elements} universe: electromagnetic-gravitational schemes.) r. a. m.) physiology (see 21.554)——much new knowledge has been gained in practically every branch of phvsiology in the period 1910-26. more and more attention is coming to be paid to the chemical aspects of the subject. nature of muscular contraction—although the energy upon which muscular contraction depends comes ultimately from that locked away potentially in the food, the process by which it is set frec is of a fundamentally different nature from that of a heat engine. the amount of heat derivable from the potential energy of the tension which is developed during the initial proc- ess of contraction may be about equal to the amount which is actually set free, an efficiency which far exceeds the possibilities of a heat engine (a. v. hill). the efficiency of the entire process of contraction is of course much less than this, although it is also considerably greater than that of a heat engine. this tension, instead of being degraded to heat, may do me- chanical work by the muscle contracting, and during the con- traction phase there is no evidence that combustion ts occurring; thus no oxygen is used up, and contraction can occur equally well in the entire absence of oxygen as in its presence. the only demonstrable chemical change that occurs during contrac- tion is that glycogen disappears and an equivalent quantity of lactic acid makes its appearance (meyerhof). the actual con- traction is apparently dependent on the sudden conversion of some of the glycogen of the muscle into lactic acid, which brings about a change in the surface tension at the interface between the sarcoplasm and the muscle fibrils. at the end of the con- traction phase the muscle possesses less potential energy, and during the next, or recovery, phase this energy is restored through a part (four-fifths) of the lactic acid which was produced during the contraction phase being built up again into glycogen, by energy which is supplied by oxidation of the remaining part (one-fifth) of lactic acid. a. v. hill has shown that the amount of heat which is given out in a complete cycle of contraction is only 19% of that which would be given out were all of the lactic acid produced and removed during the complete cycle of contraction oxidised. at the end of a complete contraction in the presence of oxygen there ts therefore less glycogen than at the start, but the amount of lactic acid is unchanged. during the recovery process alone 145 oxygen is used up and co, produced, and this combustion proc- e3s is accompanied by a further liberation of heat which has been found to be 1-5 times greater than that liberated during the contraction phase. the evidence supporting this theory of muscular contraction depends on thermometric measurements of isolnted muscles made by a. v. hill and his collaborators, by the use of very sensitive thermopiles and on chemical analyses’ by hopkins and fletcher and, more recently, by meyerhof. the theory is summed up in the following scheme: contraction 1 gr. glycogen gr. lactic are gent energy +2096 relaxation 1 gr. lacticacid—sodium lactate/ cal. (1). 0-19 er. lactic acid -~co2+h20+684 cal. (exo- thermic). o-81 er. lacticacid—-0-8 glycogen ~—240 cal. (endothermic, =444 cal. (1-5). the net result being that (296+684—240)= 740 cal. of energy are liberated with a loss of 0-19 gr. glycogen. it is also evident that the recovery heat production is 1-5 times greater than the initial heat production. since these experiments on isolated frog muscle show that oxygen is required to restore the energy material (glycogen), it is to be expected that strenuous exercise in the intact animal will result in the accumulation of lactic acid in the muscles, because oxygen cannot be supplied to them, by way of the blood, quickly enough to oxidise the acid. it has been shown (a. v. hill, etc.) that the increased oxygen intake during rapidly performed, hard exercise, such as a quick “ mark time’ movement of the legs, is relatively small when compared with the amount which is required for a considerable time after it. this “ oxygen debt ” is for the purpose of oxidising the lactic acid which accumulated in the muscles while the violent contractions were going on, and it may last for over an hour following exercise of less than one rninute’s duration. it falls off quickly immediately after the exercise, and then very slowly. it can be shown that the total excess or oxygen inspired, over the resting requirement of the body, in the performance of quickly exhausting exercise is just sufficient to oxidise an amount of lactic acid which, by accumulating in the muscles, would raise the percentage in them to the fatigue maximum which is actually observed, by chemical analysis, to occur. some of the lactic acid also overflows into the blood, so that some appears in the urine, but the greater part is removed by gradually going back into the tissues, where it is oxidised, this process being probably the cause for the long-drawn-out pay- ment of the debt. during moderate exercise, as lactic acid accumulates in the muscle, the oxygen intake becomes greater, so that after a while a steady state becomes established, in which just sufficient oxygen is being absorbed to keep the lactic acid at a constant level, and so long as the latter is not produced at such a speed that the oxygen intake cannot keep pace with it (which is largely dependent on the adaptive process of the circulation), the exercise may be kept up for a long time. leon- ard hill had previously demonstrated the improvement in stay- ing power which results from breathing oxygen during muscular exercise, so that athletic training consists essentially in learning how to bring about the steady state. increased breathing and the appearance of fixed acid in the blood both combine to cause a large excess of co: to be expired, so that the respiratory quotient, coq., during hard muscular work may rise from its resting o2 value of about o-8 to over unity. for a short period after the exercise the quoticnt may rise still higher, because the excess oz intake falls off relatively more quickly than the co, output, which must remain high so as to bring the h-ion concentration (ch) of the blood down to the normal level. the maintained hyperpnoea during exercise is mainly due to this increase in ch. at a later stage, when breathing has returned to normal, the base, which is gradually set free, because of oxidative removal of lactic acid, combines with co, and so causes the output of this gas to become rela- tively reduced, giving a low respiratory quotient. when the fotal oz excess intake and the total co. excess output are deter- oxidative recovery 146 mined during short periods of exercise (7.e., both during and following it), the interesting fact has come to light that respira- tory quoticnt equals about 1, which indicates that carbohydrate must be the source of the energy of contraction in the intact animal, just as with isolated muscle. when the exercise is more prolonged the quotient falls below unity, since o. has to be ‘retained in order to convert into carbohydrate such substances as fat, which contain relatively less oxygen. this process prob- ably occurs in the liver.! the capillary circulation.—since they are composed of thin flat endothelial cells placed side by side, the capillaries have been considered incapable of dilating or contracting independ- ently of changes in the pressure of the blood flowing in them, brought about by variations in the calibre of the minute arteri- oles. the first to observe independent alterations in the calibre of the capillaries was stricker (1865) and this was confirmed by roy and graham brown (1879). convincing evidence was furnished by dale and richards, who showed that the capil- laries dilate while the arterioles constrict during the depressor action of histamin (b-imin-azolyl-cthylamine), whereas the arterioles alone dilate with acetyl choline. when the rate of outflow was measured in a perfused preparation of the mesen- teric blood-vessels, these observers found that acctyl choline always caused dilatation, whereas histamin caused constriction, although both lowered the arterial blood pressure. ‘they also observed that a small close of histamin, o-or mg., caused a flushing of the denervated paw, while acetyl choline had no effect, indicating that the former drug had specifically dilated the capillaries. it was later possible to explain the condition of shock following larger doses of histamin as due to extensive dilatation of the capillarics, on account of which the blood stagnates in them. while the results of these rescarches made it necessary to postulate alterations in the calibre of the capillaries that are independent of changes in that of the arterioles, they did not furnish direct evidence that this occurs. krogh examined microscopically the superficial capillaries of the muscles in frogs and mammals, using strong reilected light as a source of illumi- nation. in resting muscles the capillaries are relatively few in number, and so narrow that the red corpuscles can pass along them but slowly and, often, only after marked distortion in shape. after activity, on the other hand, many more capillaries become visible, and the blood flows rapidly through them. as the circulation returns to the resting state, the capillaries again become narrower and many disappear from view; but even in a group derived from the same arteriole all do not behave alike, indicating that the degree of contractility varies. after the con- gestion caused by the irritation of pinning out the tongue of the frog subsides, many of the capillaries disappear from view. krogh observed that scratching the surface of the tongue along the course of a small vein might cause a capillary, previously invisible, to become opened up so that corpuscles moved into it. if now the mechanical stimulus was applied in a line just in front of the end of this branch, the dilatation gradually extended, until at last a visible capillary. had become formed of sufficient length to join with an arteriole, when the previously stagnant column of blood corpuscles immediately changed into a quickly flowing stream from arteriole to venule. this contractility of the capillaries is believed to depend on the presence of cells (rouget cells) with numerous protoplasmic branches which encircle the endothelium of the capillary walls. the tone of the capillaries is controlled partly by hormones and partly by nerves. krogh found that marked local dilatation of the capillaries of the frog’s tongue can be induced particularly with epinephrin. capillaries in other regions may, however, be refractory towards epinephrin. he has also offered evidence to show that the normal tone is maintained by the presence of some constituent of blood plasma. this substance can be dialysed, 1a. v. hill and his co-workers have also published numerous papers bearing on the physical aspects of muscular contraction, but the technical details are such that it is impossible to give a con- densed account of the results. physiology and it withstands heat. it bears many resemblances to pituitrin. there is also evidence of control through the nerves. hooker in 1920 showed that the capillaries in the cat’s ear become con- stricted by stimulation of the cervical sympathetic. the red area which becomes developed on the skin of man by drawing a pointed instrument along it is due to dilatation of both arterioles and capillaries, through a reflex action which is set up by the stimulation of the pain receptors. the retlex arc in these cases involves the nerve centres in the spinal cord, since the reaction is abolished by cocainisation of the skin, or by section of the sensory nerves or roots. irritation of the tongue of the frog is also followed by the development of a hypernemic zone, but the reaction is not abolished by section of the lingual nerve, so that it cannot be a true reflex. on the other hand, it is abolished by cocainisation or by degeneration of the peripheral nerves, so that some form of so-called axon reflex must be involved. the response of the capillaries and arterioles to local stimuli varies greatly in different vascular areas, and in different species of animal. capillaries also react toward changes in temperature, and they are sensitive to light. the erythema which is set up on the human skin by exposure to ultra-violet rays only disappears gradually and is followed by desquamation of the epidermis and by pigmentation. the regulation ef the reaction of the blood.—this or its h-ion concentration (expressed as ch, or for convenience the negative exponent phl) can be measured, either electrometrically (hydro- gen electrode) or colorimetrically. in the latter method, the unclotted blood is placed in a small dialyser which ts surrounded by a perfectly neutral (ph7) isotonic saline solution. after a few minutes the solution assumes the same ph as the blood, and this can be measured by adding to it an indicator, such as phenol- sulphonephthalein, which changes in tint at a ph of about 7, and then comparing the tint with those produced in a series of phosphate solutions of varying, known phi’s, containing the same concentration of indicator. the colorimetric method gives a slightly higher p¥i (blood more alkaline) than the electro- metric. while in the body arterial blood is slightly alkaline, its pit by the electrometric method being 7-35~7-4 and by the colorimetric 7-6. it is maintained practically constant, but it tends to become less alkaline (i.e., ph lower) when large amounts of fixed acid enter it, as after violent muscular exercise (lactic acid) or in diabetes (oxybutyric and acetoacetic acids). this tendency is, however, compensated for by stimulation of the respiratory centre, so that co, is expelled from the blood in the lungs. the condition thus established is called compensated acidosis, and it is characterised by the blood being unable to take up as much co, as the normal, when exposed to various partial pressures of this gas. its a/lkuline reserve is said to be lowered. when coz is deliberately blown off from the blood, by forced breathing, a relative excess of base comes to exist in the blood—alkalosts—so that an excess appears in the urine, making it alkaline in reaction. both acidosis and alkalosis are asso- ciated with characteristic symptoms. the oxygen and carbon dioxide of the blood.—for investi- gating the factors which govern the transport of co, and o, by the blood, use is made of dissociation curves, which depict the relationship between the amounts of gas absorbed at various pressures. when cos is added to blood it combines with base (na) in the plasma to form nahcos;. the na is derived partly from nacl and partly from na-protein, thus: nacl+h.,co;= nalhico; + hci; and na-protein + h2co;= nali1co3+ h-pro- tein. since iicl cannot remain as such in the plasma it migrates through the envelopes of the red corpuscles to re- act in their interior with the potassium salts of phosphoric acid and haemoglobin thus: hcl+k2hpo,= kh,po,+ kcl; and f{c]+ k-haemoglobin = kcl-+-h-haemoglobin. in virtue of these reactions the coz is absorbed without significant changes in ph (buffer action), and the plasma can take up considerably more co: when corpuscles are present than when they are absent. pure plasma also absorbs co, but in an entirely different man- ner from that of a solution of bicarbonate, because of the protein present in it (see above equation). physiology when haemoglobin combines with oxygen, its acidity is increased so that it attracts more base and thereby libcrates some h:cos from bicarbonate. consequently, the cos dissocia- tion curve for arterial blood is lower than that for venous blood. such a process occurs in the lungs, thus facilitating the removal from the venous blood of its co.. on the other hand, the loss of o, from the blood, which occurs in the tissues, causes oxyhaemo- globin to be replaced by the less acid, reduced haemoglobin, so that the absorption of co, is facilitated by some base being set free. not only do these changes in os content alter the co,- carrying power of the blood, but changes in cos, by affecting the ph, also influence the oy-carrying power of the haemoglobin. the migration of o, which occurs from the blood into the tissue cells in the capillaries is therefore due, not only to its attraction because of the low oxygen pressure in them, but also because co, migrates into the blood so as to lower ph. a quantitative relationship therefore exists in blood among the following: (1) the free o; (2) combined oz (oxyhaemoglobin); (3) free cos; (4) combined co. (nalicos); (s) ph); and (6) nacl of plasma. l. j. henderson, to whom much of our knowledge of the reaction of the body fluids is due, has shown that the relation existing among these six variables is such that if any two are known the remaining four can be computed, and he has expressed these relationships in graphical form. mountain sickness —certain characteristic symptoms, known as mountain sickness, supervene at high altitudes. ‘the impor- tance of the problem does not depend on there being any par- ticular practical value in knowing how to prevent the establish- ment of the condition, but rather because the general disturb- ance of the bodily mechanisms to which the symptoms are due furnishes an opportunity, by comparison with the normal, to determine the relative importance of certain physiological adap- tations. it is now clearly recognised that reduction in the oxygen pressure, clue to the rarefaction of the air, is the underlying cause of the symptoms, several features of which demand attention. the symptoms do not become developed during short stays in the rarefied atmosphere, and they are therefore not usually observed in short flights to great altitudes in flying-machines or balloons. they do not, as a rule, become acute on reaching a high elevation on a mountain by railway until after a day or so, unless muscular exertion is attempted. the acute symptoms are severe enough to incapacitate the individual, and they include headache, a sense of great fatigue, sleeplessness, often nausea and vomiting, with various circulatory and respiratory symp- toms, including cyanosis. after one to four days the acute symptoms disappear but less definite ones remain, such as men- tal sluggishness, readiness to fatigue, breathlessness on moder- ate exertion, sleeplessness, etc. in peoples who have lived for long at altitudes such as those obtaining in the andes (14,000-16,000 ft.) the bodily functions are apparently quite normal, except that muscular exertion leads to breathlessness more readily than it should. there are also cer.ain minor deviations from the normal, such as cyanosis (blueness), tendency to clubbed fingers and a change in the shape and the diameters of the thoracic cavity. the most sig- nificant feature of mountain sickness from the physiological standpoint is the disappearance of the acute symptoms after a few days’ acclimatisation. in an anglo-american expedition to pike’s peak, under the leadership of j. s. haldane, f.r.s., in 1912, the important conclusions were drawn: (1) that the symptoms are due to anoxaemia (that is, a subnormal pressure of oxygen in the blood supplying the tissues); and (2) that acclimatisation depends on increased breathing and on the development by the pulmonary epithelium of the power to secrete oxygen into the blood from the air in the lungs. under physiological conditions at sea-level this secretion of oxygen does not take place, since diffusion is adequate to determine the passage of oxygen into the blood. a more recent expedition (1921-2), under the direction of mr. j. barcroft, f.r.s., to the peruvian andes failed to obtain evidence of any secretion of oxygen by the pulmonary epithelium at an altitude of 14,000 feet. acclimatisation was found to depend 147 on (1) an increase in lung ventilation, which raises the tension of oxygen in the pulmonary alveoli by 10-12 mm. and, therefore, also the tension in the arterial blood; (2) alteration in the power of the blood to absorb oxygen, so that at a given pressure of this gas a larger percentage is absorbed (q.-dissociation curve); (3) decided increase in the percentage of red corpuscles, and there- fore of haemoglobin, in the blood. the greater amount of haemoglobin increases the store of loosely bound oxygen carried into the capillaries, so that the venous blood is more saturated with oxygen than would otherwise be the case; but the chief advantage of this adaptation is a secondary one, the significance of which was demonstrated in subsequent experiments, in which it was found that when blood removed at sea-level was deprived of some of its cos, separated into plasma and corpuscles by centrifuging, and these two parts then recombined, so that the percentage of corpuscles was the same as that of persons accli- matised to rarefied air, the dissociation curve for qo. assumed the same form as in the blood of persons acclimatised to high altitudes. no decided alterations in the reaction of acclimatised blood could be detected, although the tension of cq, in it, be- cause of the hyperpnoea, was lower than at sea-level. the function of the parathyroid gland.—removal of the four parathyroid glands is soon followed by the appearance of symp- toms which are quickly fatal. the condition is called parathy- roid tetany. carnivorous animals are far more susceptible than herbivorous, and in the former substitution of the usual diet by one of milk and bread prevents the onset of the symptoms. ad- ministration of calcium can also prevent their development. when one of the glands is left no acute symptoms may develop, although general nutritional disturbances gradually become evident, such as faulty development of the bones and teeth in young animals and a low assimilation limit for sugar. two chemical changes in the blood have been found to be associated with parathyroid tetany: (1) a deficiency in the free calcium and (2) accumulation of guandin and its appearance in the urine. the above symptoms may be removed by grafting a para- thyroid gland from the same species of animal, thus suggesting an internal secretion, and collip prepared from the glands an extract, parathormone, which is capable, when injected sub- cutaneously into parathyroidectomised dogs, of promptly re- moving the symptoms of tetany. after one injection the animals remain free of the symptoms for about 60 hours; but if the injec- tions be repeated the animals may remain permanently free of them and the blood calcium rises to, or above, the normal level (tromg.%). repeated injection of the extract into normal dogs also causes the blood calcium gradually to increase, and when a certain level (about 20mg. ca. per roo c.c. blood) has been reached characteristic symptoms supervene, consisting at first of weakness and hyperpyrexia and, later, of vomiting and diar- thoea, often accompanied by the appearance of blood in the vomitus and stools. the blood also becomes very viscid and darkly venous in colour, and the usually fatal outcome is prob- ably due toa failure of the blood to circulate through the capil- laries because of its stickiness. herbivorous animals, such as mice, rabbits, guinea-pigs, do not show these symptoms on in- jecting parathormone (macleod and taylor). the neuro-muscular system—a_ valuable experimental analysis of the reflexes concerned in maintaining the position of the animal body while at rest and in movement has been con- tributed by magnus. it will be recalled that a certain condition of extreme tonic contraction of the extensor muscles supervenes upon removal of the cerebrum (the decerebrate rigidity of sherrington). it is now established, by the method of section at different levels of the brain, that the centre concerned is located in the medulla oblongata above the level of calamus scriptorius but below that of the red nucleus. this centre excites increased tone of the extensor musculature, and its effects are counter- acted, in the intact animal, by impulses coming from another centre located in the red nucleus, which excites their antagonists, the flexors. when an animal in decerebrate rigidity is placed in the standing posture it can maintain this attitude, but it cannot retain it if disturbed. 148 on the other hand, if the section be anterior of the red nucleus, the animal can right itself if displaced from the standing posture. working with preparations of these types magnus and his co-workers have shown how reflexes initiated from different sense-organs, such as the labyrinth, the eyes and the proprio- ceptive nerves of the muscles, interact among one another to bring about the various postural reactions of the body. magnus distinguishes between sfatic and stato-kinetic reflexes. the former include the postural reactions when the body is at rest, and they may be reflexes of pose, in which the body remains fixed in a certain position; or righting reflexes, which are those which come into play to restore the pose after it has been disturbed. stato- kinetic reflexes are produced by the actual movement of the body rather than the position which results from this movement. as an example of the methods employed in these studies, refer- ence may be made to experiments illustrating tonic neck re- flexes and tonic labyrinth reflexes. to demonstrate the former the labyrinth is removed in a decerebrate preparation, and it is found that when the head is moved so that certain of the neck muscles are put on the stretch and others relaxed the limbs assume definite positions which are characteristic for each posi- tion of the head, but which are not the same for the fore and hind limbs nor for those of opposite sides of the body. to demon- strate labyrinthine reflexes the labyrinths are left intact, and movements of the muscles of the neck are prevented by encasing the neck of the preparation in plaster of paris. variations in the orientation of the animal then result in poses of the limbs which are characteristic for each position, but in this case all four limbs behave alike. destruction of the labyrinth abolishes these reactions. glutathione —the very difficult problem of the mechanism of tissue oxidations has been considerably elucidated by the dis- covery of sir f. gowland hopkins that a comparatively simple substance called glutathione can be prepared from various tis- sues, although not from the blood or connective tissues. chemi- cally, it is a depeptide of cysteine and glutamic acid, and it has recently been synthesised by stewart and tunnicliffe. in the reduced form its general formula may be written g:-sh, where g: represents glutamic acid and sh cysteine. when it is oxidised the following reaction occurs: 2 gsh-—-g-s-s-g+h2. it is probable that a peroxide is formed during its oxidation, and if this occurs in the tissues the peroxide would be available for complete oxidation. much attention has also been given to the hypothesis of wieland that the oxidation of the majority of substances con- sists essentially in the removal of hydrogen, rather than the addition of oxygen. as applied to tissue oxidations, this means that enzymes called hydrogentransportases act by transferring hydrogen from one oxidisable substance (hydrogen donator) to substances which become reduced (hydrogen acceptors). for many of the studies in this field methylen blue has been used as the acceptor, the speed of the reactions being measured by the time required to effect its decolorisation in vacuo. . bibliography.—williams and wilkins, physiological reviews (baltimore); a. krogh, the anatomy and phystology of the capil- laries (1922); j. j. r. macleod, physiology and biochemistry in mod- ern medicine, 4th ed., st. louis (1922); sir w. h. bayliss, prin- ciples of general physiology, 4th ed. (1924); c. a. lovatt evans, recent advances in physiology (1925); j. j. r. macleod, carbohy- drate physiology and insulin, ‘‘ monographs in physiology ” (1926). (j. j. r. mac.) piano: sce musical instruments. piave: see vittorio venito, battle of. picasso (1881- ), spanish painter. pablo ruiz was born in malaga, spain; he took the name of his mother, picasso. in his sixth year the family moved to barcelona, where his father was a professor at the academy of arts, and where the son held his first exhibition. a spaniard living and working in paris, he is perhaps more typical of the present age, more deeply influenced by the uncertain and tortured spirit of the times, than any other painter alive. during the years 1906-12 he was associated with georges braque in developing cubism, a method of painting which, in spite of excesses and debase- piano—pilnyak ments, has definitely modified the world’s conception of that art. in picasso’s cubism painting for the first time becomes deliberately conscious of the new world of the machine, and of the modifications in the eye made by familiarity with all its complicated and exact patterns. the logical conclusion of his theory was a kind of painting which used form and colour not to imitate nature but to create a plastic world of its own that would have no connection with the world of nature, that would in fact be a pure and abstract art like mathematics. but picasso abandoned cubism before it reached that logical conclusion which his strain of spanish mysticism had led him to visualise so differently. herein lies the clue to his astoundingly fertile but unstable genius. compared with cezanne and el greco, who were his most important masters, he lacks that staying quality, that capacity to endure, which is one of the requisites of great art. lis sensory receptiveness is inexhaustible, but his creative power is limited by his lack of resistance. since his desertion of cubism, he has gone back to ingres, and his recent work shows sheer virtuosity of draughtsmanship without any great emotional quality. picasso’s numerous works are mostly to be found in private collections. (see painting.) bribliography.—the fullest account of picasso is found in maurice raynal’s picasse (1922). other works are guillaume apollinaire, ‘‘ picasso,’”’ la plume (may 1905); les peintres cubistes (1913); fritz burger, cezanne und hodler (1913); max raphael, von monet 2 picasso (1913); jan gordon, afedern french painters (1923); paul westheim, die architektonik des plastischen (1923); elie faure, history of art (1924). pickering, edward charles (1846-1919), american physicist and astronomer (see 21.528), died at cambridge, mass., feb. 3 1919. pickford, mary (18093- ), american motion picture actress, was born at toronto, canada, april 8 1893. she made her first appearance on the stage at the age of five with the local valentine stock co., and when eight went on tour, playing the part of jessie, the little mother, in the fatal wedding. she came to new york under the auspices of belasco, creating the part of betty warren in the warrens of virginia. wer first motion picture work was undertaken with d. w. griflith as an extra, but she returned for a time to belasco, taking the part of juliet in a good little devil at the republic theatre in new york. in 1913 she came back to the screen with famous players co, and rose to the first rank. in 1916 the mary pickford film corp. was organised and she received a salary higher than that paid to any other motion picture actress. in 1918 she became an independent producer and went to california. in 1919 she was the prime mover in the formation of the united artists corp. or ‘‘ big four,” composed of miss pickford, charles chaplin, douglas fairbanks and d. w. griffith. taking juvenile char- acters, miss pickford was for long the most popular screen actress in the world. among the best known and most artistic of her pictures were tess of the storm country, little lord fauntleroy and dorothy vernon of haddon hall. she married douglas fairbanks, the motion picture actor and producer, march 28 1920. | . pietermaritzburg, natal, s. africa (sce 21.592), had a population (1921) of 25,160 and with the suburbs of 36.023. something like half (17,998) were whites. in 20 years the white population had increased by 3,400 only. maritzburg, as it is commonly called, retains its pleasant, dignified character, has many fine public buildings, and is the religious, educational, professional and agricultural centre of natal. up to 19ro the natal parliament, abolished at the establishment of the union, met here; it is now the meeting place of the provincial council, the seat of an anglican bishop, and of the natal division of the supreme court. university college is a constituent col- lege of the university of south africa. its agricultural shows are noted for their excellence. fort napier, where thousands of german prisoners were interned during the world war, is now used as quarters for government and railway servants. pilnyak (1804- ), russian novelist. boris andreevich vogau, who later took the pen name of pilnyak, was born sept. 29 1894 in mojaisk, moscow province. his childhood and early pilsudski youth were spent on the volga and among the peasants and the land administration “ intellectuals.” he studied economics at the moscow commercial institute and began publishing stories in 1915. during the bolshevik revolution pilnyak lived in mos- cow and also travelled through russia studying the new condi- tions. in 1923 he visited england and germany. his works deal with the first chaotic stage of transition from the old tsarist russia to the “ new world” of the soviet republic. he is the most prominent figure in post-revolutionary fiction. his sympathies are with the peasants as opposed to the town and his stories are deliberately fragmentary and read like diaries and chronicles. pilsudski, joseph (1867- }, polish soldier, was born in nov. 1867 in zulow (zulowo), county of vilna (wilno) of an ancient family tracing their origin from the lithuanian [princes of ginet. he was educated at the gymnasium of wilno and attended the medical faculty at the university of kharkov. in 1887 pilsudski was involved in an anti-tsarist plot and sentenced to five years’ penal servitude in eastern siberia, although the trial clearly established his innocence and his deprecation of terrorist methods. in his exile he learnt to know the russians well. he returned to wilno in 1892 and commenced his political activities there. as regards his convictions he was a socialist, but he realised that a democratic state, free from political oppression was necessary in order to safeguard the natural development of the social system; consequently the political independence of poland was introduced into the pro- gramme of the pclish socialist party (p.s.p.) formed by him. “ romanticism of aims—realism of means ”- -that is how he described his creed. and methods. in 1894 he commenced the publication of the secret paper robotnik (the workman) and during the next ten years this paper voiced the most radical and outspoken opinions in poland. robotnik was edited, printed and distributed by pilsudski him- self. the risk of penal servitude for life did not deter him; wherever he went he inspired confidence and encouragement. his courage, keen sense of humour, attractive personality and good breeding made him the idol of the working classes; he was re- vered by the intelligentsia for the tenacity of his convictions, for his fearlessness and his iron will. in 1894 he married mlle. marie juszkiewicz; and assisted by his wife gradually increased the scope of his political activities. armed resistance against the atrocities of the russian govt. was introduced into the programme of his party. meetings and demonstrations were, in consequence, protected against the police and the military by armed detachments of workmen. every year on may 1 blood flowed down the streets of polish cities, reminding the nation that there were principles worth dying for by a “ sudden and untimely death.” in rgo0o pilsudski and his wife were arrested in the offices of the robotnik in ledzz and for a year he was kept in a special cell in the notorious “ tenth pavilion ’’ of the warsaw citadel. in order to avoid a life sentence pilsudski simulated insanity, and was, in con- sequence, transferred to the st. nicholas hospital in st. peters- burg (leningrad). on may 13 1901 he was rescued, the result of an ingenious plot of the polish socialist party. he lived in london for some time and returned to cracow in 1902. pilsudski’s attention next became concentrated on the organi- sation of “armed resistance.”? lack of munitions, however, frustrated his plans for an insurrection during the russo- japanese war. fle went to japan in order to enlist her support, but met with indifference from the japanese government. in spite of the failure of his mission, pilsudski continued to organise his men by private means. after the russian revolution of 1905 and the convocation of the duma in st. petersburg polish revolutionary activities were discontinued, but the russian constitutional govt. continued to pursue the pclicy of its prede- cessors with regard to poland. pilsudski transferred his head- quarters to cracow and lwow and commenced his activities amongst the refugees from the russian provinces of the country. the seemingly chimerical idea of a “‘ private polish army ” was conceived there. an officers’ school was established in lwow 149 and branches of the ‘ sharpshooters ” (strzelec) were formed throughout galicia. in a lecture delivered in feb. 1914 before the geographical society in paris, pilsudski prophesied the imminence of the world war; he expressed the opinion that the ideal conclusion of such a war, from the polish point of view, would be for austria and germany to conquer russia, and for france to win a victory over germany. true to his opinions, he sided with austria when war broke out. the total strength of his ‘ army ” was 3,000 infantry and a squadron of cavalry insufficiently armed and equipped; the remaining 7,c00 of his men were dispatched to hungary by the austrian general command. pilsudski resisted vigorously every attempt of the central powers to employ his own legions outside the frontiers of poland. when, in nov. 1914, the germans attempted to send the legions over to the western front, he broke through the russian columns and, in disobedience to austrian orders, returned to cracow. his brigade took part in numerous battles in which it exhibited great bravery and exemplary discipline. as a leader of his troops pilsudski was unsurpassed. calm, brave, simple and devoted to his men, he became the idol of his subordinates. his mere presence in the trenches inspired the troops with the hope for glory and a cer- tainty of victory. when, after the collapse of the brusilov offensive, russia was virtually conquered, pilsudski turned against the remaining partition powers, 7.c.. germany and austria. in july 1916 he resigned the command of the polish legions in consequence of the abuses of the german and austrian occupation authorities in polish territory. at the same time he sought to establish relations with france and great britain through his colleagues, mam. sokolnicki and narutowicz. his attitude, which was quite natural, was, however, met with distrust by the allied powers. on nov. 5 1916 the independence of poland was proclaimed by the central powers and vilsudski accepted the position of min- ister of war in the newly formed council of state. within a short time he formed the semi-secret polish military organisa- tion, 7.c., polska organizacia wojskowa (“ p.o.w.”’), which spread throughout the country and was instrumental in disarming germans and austrians in 1918. when the polish legions in russia, commanded by gen. musnicki, proclaimed pilsudski their spiritual leader, and when his own legions refused, in july 1917, to take the oath of “ fra- ternity of arms with germany and austria,” pilsudski was arrested by the germans and imprisoned with his chief-of-staff gen. sosnowski in the fortress of magdeburg, whence he was released in 1918 by the german revolutionary authorities. he arrived in warsaw on nov. 4 and completed the disarmament of the armies of occupation. the regency council, established by the germans, resigned in his favour and all military organisa- tions in the country submitted to his command. an efficient and disciplined army was soon formed. with this army pilsudsk1 maintained the independence of poland, which was menaced on all frontiers by the bolshevists, lithuanians, ukrainians, czechs, and germans (in silesia) and laid the foundations of a strong, democratic state. vested with dictatorial powers, he, like a modern washington, summoned the constituent diet elected by general ballot. he gave his country everything which he thought was necessary for its constitutional development; like a lion he guarded its inviolability and its prestige. his great mind, his sense of justice, his deep and disinterested love for his country gained for him the admiration of his people. his election as chief-of-state was unanimous; and the army conferred upon him the supreme honour of first marshal of poland. in foreign politics marshal pilsudski proved himself to be a cautious and far-seeing statesman. his military genius was exhibited particularly during the war of 1920. believing that poland ought to pursue the traditions of its “ golden age” (14th, rsth and 16th centuries), he undertook the expedition to kiev in 1920. he captured kiev in order to hand it over to poland’s ally the ukraine, in the same way as he took dunaburg to hand it over to latvia. unfortunately, the ukrainians were too weak to take advantage of pilsudski’s victories; his plans for 150 a polish-ukrainian federation failed and the polish troops retreated from kicv. the strategic aim was, however, achieved; the southern flank of the russian army which was to attack lwow and the oilfields was completely disorganised, and thus the bolshevists were forced to attack from the north. their numeri- cal superiority gave them initial advantages. disregarding the opinions of alt his military advisers, pilsudski concentrated along the river wieprz his devoted regiments and by a lightning attack, which he led himself, broke through the russian front and dispersed the bolshevist hordes collected round warsaw, where they expected an “ easy victory.”’ pilsudski’s victory saved not only poland but the whole of europe from a new war and conflagration. personally modest, although grand in his ideas, joseph pil- sudski retired from public life when he became aware that his actions and advice evoked distrust and intensified party fecling. his retirement did not weaken factional wrangling, however. on the contrary it intensified the decay of parliamentary life and multiplied cases of administrative corruption. when this trend of events became a menace to the republic, marshal pilsudski came to the conclusion that, as the creator and spiritual leader of the modern polish state, he could no longer remain inactive. supported by his devoted army, he demanded the strengthening of the authority of the president, a greater measure of govern- ment independence from a faction-ridden parliament and the impeachment of all persons guilty of corruption, regardless of their standing or party support. marshal pilsudski’s opponents succeeded in gaining the for- mal support of wojciechowski, president of the republic. the military demonstration undertaken by the marshal on may 12 developed into a three days’ army conflict in the strects of war- saw resulting in the resignation of the president. the national assembly, convoked by his successor, monsieur rataj, marshal of the dict, elected, by a great majority, a new president in the person of joseph pilsudski. the results of the election were hailed with tremendous enthusiasm throughout the whole country, particularly among the peasant and working classes. pilsudskt, however, desirous of devoting himself entirely to the army, did not accept the high office and recommended prof. ignacz mosiekt as the most suitable candidate. the latter was elected president and called upon monsieur bartel to form a government which would undertake internal reforms on the lines proposed by pil- sudski. the marshal himself accepted the office of minister of war and chairman of the supreme army council. — (w. sr.) pirandello, luigi (1867- ), italian dramatist and novelist, was born june 28 1867 on a country estate near girgenti (sicily). he first went to rome at the age of 19, staying there until 1891, when he went to germany and graduated in philosophy at the university of bonn. he subsequently re- turned to rome and taught at the girls’ high school until 1923. his first literary essays were in verse, a volume entitled mal giocondo published in 18809, followed by a poem pasqua dt gea (1891) and elegie renane (1895). another sicilian writer, luigi capuana, persuaded him to devote himself to fiction, and in 1894 he published his first novel, l’esclusu, in which his some- what bitter realism already finds expression. besides the comic novel, z/ iurno, he began to publish short stories in ever- increasing numbers, the somewhat painful humour of which soon attracted public attention: amori senza amore (1894), ouando ero matto (1903), beffe della morte e della vita (1902, 1903), biasche e nere (1904), etc. in 1904 his most celebrated novel, i/ fi maetlia pascal, appeared, the story of a man, who having shammed being dead, tries in vain to begin his life anew in a different atmosphere and under another name, but fails lamentably. other collections of short stories followed: ferma bifronte (1906), la vita nuda (1910), terzettt (1912). he set forth his artistic creed in two volumes entitled -lrfe ¢ sciensa (1908). in 1913 his novel, i veccht e 7 giovani, describing the drama of italian life after the risorgimento, was published in the russegna contemporanea. other volumes of short stories appeared between 1014 and 1926, such as la trappolu (1915), ua cavallo nella luna (1918), if carnevale dei mortt (191g), tu ridi (1920), pirandello—pirennie and another novel u0, nessuno e centomila was published in the fiera letteraria. in 1920 he said of his own art:— t think that life is a very sad piece of buffoonery; because we have in ourselves, without being able to know why, wherefore or whence, the need to deceive ourselves constantly by creating a reality (one for each and never the same for all), which from time to time ts dis- covered to be vain and illusory .... my art is full of bitter com- passion for all those who deceive themselves; but this compassion cannot fail to be followed by the ferocious derision of destiny which condemns man to deception. this despairing outlook attained its most vigorous expression in pirandello’s plays. in his youth he had shown a certain con- tempt for the drama, but in 1912 he was persuaded by the sicilian plavwright, nino martoglio, to dramatise one of his own short stories, la aforsa,as a one-act piece. his first three-act comedy, se non cosi (1917), was produced by marco parga at milan in 1913; and then many plays—dramas and comedies—of which the most celebrated are il berretto a sonagli, liola (1917), cosi e se tt pare (1918), l’nomo, la bestia e la virtit (1918), afa non e una cosa seria, come prima, meglio di prima, sei personaggi in cerca d'autore, l’imbecille, enrico [v., vestire gli ignudi (1918), la vita che ti diedi, l'altre figlio, ciascuno a suo modo, la sagra del signore dclla nave, la giara. pirandello’s dramatic art was at first criticised for being too “ cerebral,” for not seeing life as it really is and for arbitrarily deforming it. the roman critics first discovered the real mean- ing of pirandello’s ideology and the human sense of his plays. his main themes are: the necessity and the vanity of illusion, the multiform appearances, all of them unreal, of what is presumed to be the truth, man is not what he thinks he is, but he is “ one, no one and a hundred thousand,” accordingly as he appears to this person or to that, and is always <lifferent from what he creates himself in his own mind. hence the supreme catastrophe, when a moral looking-glass suddenly reveals to him the image of himself which others sce, 7.e., what he 7s to others. most of piran- dello’s plays deal with a lower middle class milieu, peopled with clerks, teachers, lodging-house keepers, etc., from whose modest vicissitudes he draws conclusions of vast human significance. typical is cosi e se vi pare, in which he proves that it is impossible to know the real truth. enrico iv’. devclops in a broader sense; that is, a drama in which we have a man who renounccs his changing, empty and vain existence to play the part of a mad- man, and pretends to believe himsclf an historical personage, henry iv. all this might be merely theatrical trickery if it were not seared by a deep anguish, characterising a philosophy which has destroyed all faith in the absolute, in reality, in any fixed limits outside individual personality. pirandello’s plays have rapidly achieved success throughout italy and abroad, and have been translated into some 15 lan- guages. in 1925 he created an art theatre of his own in rome, where new italian and foreign plays are performed, and in the summer of the same year he brought his company on a tour to england to produce his own plays in london (at the new oxford theatre), to paris, basle and 18 theatres in germany. everywhere he met with an enthusiastic reception. (s. p’a.) pirenne, henri (1862- ), belgian historian, was born at vervicrs dec. 23 1862. he first lectured at the university of liege, and in 1886 became professor at the university of ghent. ilis most famous work, histvire de belgique, of which five vol- umes had appeared in 1923, completely revolutionised the cur- rent conceptions of belgian history and nationality. starting from the origins, m. pirenne showed how, from the time of the germanic invasions, flemings and walloons were drawn to- gether by community of tradition and economic interest: the unity achieved in the rsth century under the dukes of burgundy wis not the result of a forcign domination, but of the natural development into a modern nation of the various fiefs, among which belgium was divided in the middle ages. when the belgian provinces came under foreign rule during the following centuries, their local libertics were jealously preserved by the people, until their complete independence was recognised by the powers in 1830. pistol— pittsburgh m. pirenne became chiefly known among historians as a mediaevalist, and his works on mediaeval cities and social condi- tions include les anciennes democraties des puys-bas (paris, tg10, eng. tr. 1915) recueil des documents relatifs &@ phistorre de pindustrie dru piere en flandre (with g. espinas, 4 vol. 1906-24) ind mediaeval cities: their origins and the revival of trade (princeton, 1925). m. pirenne was the first president of the “ union academique intcrnationale ’’ (1920-3) and received honorary degrees from the universities of brussels, oxford, manchester, groningen, paris, strasbourg, bordeaux, leipzig and tiibingen. (see albert, king of the belgians; belgium.)