BICHAT

bichat, marie francois xavier (1771-1802), french anatomist and physiologist, was born at thoirette (jura) on the 14th of november 1771. his father, a physician, was his first instructor. he entered the college of nantua, and afterwards studied at lyons. in mathematics and the physical sciences he made rapid progress, but ultimately devoted himself to the study of anatomy and surgery, under the guidance of m.a. petit (1766-1811), chief surgeon to the hotel dieu at lyons. the revolutionary disturbances compelled him to fly from lyons and take refuge in paris in 1793. he there became a pupil of p.j. desault, who was so strongly impressed with his genius that he took him into his house and treated him as his adopted son. for two years he actively participated in all the labours of desault, prosecuting at the same time his own researches in anatomy and physiology. the sudden death of desault in 1795 was a severe blow to bichat. his first care was to acquit himself of the obligations he owed his benefactor, by contributing to the support of his widow and her son, and by conducting to a close the fourth volume of desault's _journal de chirurgie_, to which he added a biographical memoir of its author. his next object was to reunite and digest in one body the surgical doctrines which desault had published in various periodical works. of these he composed _oeuvres chirurgicales de desault, ou tableau de sa doctrine, et de sa pratique dans le traitement des maladies externes_ (1798-1799), a work in which, although he professes only to set forth the ideas of another, he develops them with the clearness of one who is a master of the subject. in 1797 he began a course of anatomical demonstrations, and his success encouraged him to extend the plan of his lectures, and boldly to announce a course of operative surgery. in the following year, 1798, he gave in addition a separate course of physiology. a dangerous attack of haemoptysis interrupted his labours for a time; but the danger was no sooner past than he plunged into new engagements with the same ardour as before. he had now scope in his physiological lectures for a fuller exposition of his original views on the animal economy, which excited much attention in the medical schools at paris. sketches of these doctrines were given by him in three papers contained in the memoirs of the societe medicale d'emulation, which he founded in 1796, and they were afterwards more fully developed in his _traite sur les membranes_ (1800). his next publication was the _recherches physiologiques sur la vie et sur la mort_ (1800), and it was quickly followed by his _anatomie generale_ (1801), the work which contains the fruits of his most profound and original researches. he began another work, under the title _anatomie descriptive_ (1801-1803), in which the organs were arranged according to his peculiar classification of their functions, but lived to publish only the first two volumes. it was completed on the same plan by his pupils, m.f.r. buisson (1776-1805) and p.j. roux (1780-1854). before bichat had attained the age of eight-and-twenty he was appointed physician to the hotel dieu, a situation which opened an immense field to his ardent spirit of inquiry. in the investigation of diseases he pursued the same method of observation and experiment which had characterized his researches in physiology. he learned their history by studying them at the bedside of his patients, and by accurate dissection of their bodies after death. he engaged in a series of examinations, with a view to ascertain the changes induced in the various organs by disease, and in less than six months he had opened above six hundred bodies. he was anxious also to determine with more precision than had been attempted before, the effects of remedial agents, and instituted with this view a series of direct experiments which yielded a vast store of valuable material. towards the end of his life he was also engaged on a new classification of diseases. a fall from a staircase at the hotel dieu resulted in a fever, and, exhausted by his excessive labours and by constantly breathing the tainted air of the dissecting-room, he died on the 22nd of july 1802. his bust, together with that of desault, was placed in the hotel dieu by order of napoleon. bichromates and chromates. chromium trioxide dissolves readily in water, and the solution is supposed to contain chromic acid, h2cro4; the salts of this acid are known as the chromates. in addition to these normal salts, others exist, namely bichromates, trichromates, &c., which may be regarded as combinations of one molecular proportion of the normal salt with one or more molecular proportions of chromium trioxide. the series will thus possess the following general formulae:-- m2cro4 m2cr2o7 m2cr3o10 &c. (m = one atom of a normal chromate bichromate trichromate monovalent metal.) _chromates._--the alkaline chromates are usually obtained by fusion of a chromium compound with an alkaline carbonate and an oxidizing agent, such for example as potassium nitrate or chlorate. the native chrome-ironstone (cr2o3.feo) may be used in this way as a source of such compounds, being fused in a reverberatory furnace, along with soda-ash and lime, the oxidizing agent in this case being atmospheric oxygen. they may also be prepared by oxidizing chromium salts (in alkaline solution) with hydrogen peroxide, chlorine, bleaching powder, potassium permanganate and manganese dioxide. the majority of the chromates are yellow in colour, and many of them are isomorphous with the corresponding sulphates. the alkaline chromates are soluble in water, those of most other metals being insoluble. by the addition of mineral acids, they are converted rapidly into bichromates. they are easily reduced in acid solution by sulphuretted hydrogen, and also by sulphur dioxide to chromium salts. the chromates are stable towards heat; they are poisonous, and may be recognized by the yellow precipitates they give with soluble barium and lead salts. potassium chromate, k2cro4, may be prepared by neutralizing a solution of potassium bichromate with potassium carbonate or with caustic potash. it crystallizes in yellow rhombic prisms, and is readily soluble in water, the solution having a bitter taste and an alkaline reaction. when heated in a current of sulphuretted hydrogen, or carbon bisulphide, it yields a mixture of chromium sesquioxide and sulphide. when heated with sulphur it yields chromium sesquioxide. sodium chromate, na2cro4.10(h2o), forms pale yellow crystals isomorphous with hydrated sodium sulphate, na2so4.10(h2o). it is deliquescent, and melts at 23 deg. c. (m. berthelot). by evaporation of its aqueous solution at temperatures above 30 deg. c. it may be obtained in the anhydrous condition. lead chromate, pbcro4, occurs native as the mineral crocoisite, and may be obtained as an amorphous pale yellow solid by precipitating a soluble lead salt by an alkaline chromate. it is used as a pigment under the name "chrome yellow." when digested for some time with a caustic alkali it is converted into a basic salt, pbcro4.pbo, a pigment known as "chrome red." it melts readily, and on cooling resolidifies to a brown mass, which at moderately high temperatures gives off oxygen and leaves a residue of a basic lead salt; for this reason fused lead chromate is sometimes made use of in the analysis of organic compounds. silver chromate, ag2cro4 is a dark red amorphous powder obtained when silver nitrate is precipitated by an alkaline chromate. it is decomposed by the addition of caustic alkalis, forming silver oxide and an alkaline chromate. _bichromates._--the bichromates are usually of a red or reddish-brown colour, those of the alkali metals being readily soluble in water. they are readily decomposed by heat, leaving a residue of the normal chromate and chromium sesquioxide, and liberating oxygen; ammonium bichromate, however, is completely decomposed into chromium sesquioxide, water and nitrogen. sulphuretted hydrogen and sulphur dioxide reduce them in acid solution to the condition of chromium salts. potassium bichromate, k2cr2o7, is obtained by fusing chrome ironstone with soda ash and lime (see above), the calcium chromate formed in the process being decomposed by a hot solution of potassium sulphate. after the calcium sulphate has settled, the potassium chromate solution is converted into bichromate by the action of sulphuric acid, and the salt is allowed to crystallize. it forms large triclinic prisms of specific gravity 2.6-2.7, which are moderately soluble in cold water and readily soluble in hot water. the solution is strongly acid in reaction and is very poisonous. potassium bichromate finds extensive application in organic chemistry as an oxidizing agent, being used for this purpose in dilute sulphuric acid solution, k2cr2o7 + 4h2so4 = kaso4 + cr2(so4)3 + 4h2o + 3o. on the addition of concentrated sulphuric acid to a cold saturated solution of the salt, red crystals of chromium trioxide, cro3, separate (see chromium), whilst when warmed with concentrated hydrochloric acid and a little water, potassium chlorochromate is produced. when heated with phosphorus trichloride in a sealed tube to 160 deg. c., potassium chlorochromate, phosphorus oxychloride, potassium chloride, and a complex chromium oxide (possibly cr3o6) are produced (a. michaelis, _jour. prak. chem._, 1871, ii. 4, p. 452). potassium bichromate finds application in photography, in calico-printing and in the preparation of bichromate cells. sodium bichromate, na2cr2o7.2{h2o}, may be obtained by the addition of the requisite quantity of chromium trioxide to a solution of sodium chromate. it crystallizes in hyacinth-red prisms, which are very hygroscopic and melt at 320 deg. c. _trichromates._--the trichromates are obtained by the addition of nitric acid (of specific gravity about 1.2) to solutions of the bichromates. they form rhombic crystals of a red or brown red or brown red colour and are readily decomposed by warm water, with formation of the bichromate. _perchromic acid._--by the addition of hydrogen peroxide to a solution of chromic acid, a fine blue coloration due to a perchromic acid is produced which is readily absorbed by shaking out with ether. the following formulae have been assigned to the compound:--h2o2.cro3 (h. moissan, _comptes rendus_, 1883, 97, p. 96); h2o2.2hcro4 (m. berthelot, _comptes rendus_, 1889, 108, p. 25); cr2o7.xh2o (l.c.a. barreswil, _ann. chim. et phys._, 1847 [3], 20, p. 364), and cro6.3{h2o} (t. fairley, _chem. news_, 1876, 33, p. 237). the more recent investigations of h.g. byers and e.e. reed (_amer. chem. jour._, 1904, 32, p. 503) show that if metallic potassium be added to an ethereal solution of the blue compound at -20 deg. c., hydrogen is liberated and a purple black precipitate of the perchromate, of composition kcro4 or k2cl2o8, is produced; this compound is very unstable, and readily decomposes into oxygen and potassium bichromate. similar sodium, ammonium, lithium, magnesium, calcium, barium and zinc salts have been obtained. it is shown that the blue solution most probably contains the acid of composition, h2cr2o8, whilst in the presence of an excess of hydrogen peroxide more highly oxidized products probably exist. bicker (connected by skeat with _bike_, to thrust or strike), an old english word (traced from the 13th century) implying conflict or disputation. a poetical use, from the noise, is seen in tennyson's _brook_, "to bicker down the valley."