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    "source_title": "Encyclopaedia Britannica (1911)",
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    "chunk_id": "1911:carbohydrate:144fa6156261",
    "title": "CARBOHYDRATE",
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    "verified_text": "carbohydrate, in chemistry, the generic name for compounds empirically represented by the formula c_{x}(h2o)_{y}. they are essentially vegetable products, and include the sugars, starches, gums and celluloses (q.v.). carbolic acid or phenol (hydroxy-benzene), c6h5oh, an acid found in the urine of the herbivorae, and in small quantity in _castoreum_ (f. wohler, _ann._, 1848, 67, p. 360). its principal commercial source is the fraction of coal-tar which distils between 150 and 200 deg. c., in which it was discovered in 1834 by f. runge. in order to obtain the phenol from this distillate, it is treated with caustic soda, which dissolves the phenol and its homologues together with a certain quantity of naphthalene and other hydrocarbons. the solution is diluted with water, and the hydrocarbons are thereby precipitated and separated. the solution is then acidified, and the phenols are liberated and form an oily layer on the surface of the acid. this layer is separated, and the phenol recovered by a process of fractional distillation. it may be synthetically prepared by fusing potassium benzene sulphonate with caustic alkalis (a. kekule, a. wurtz); by the action of nitrous acid on aniline; by passing oxygen into boiling benzene containing aluminium chloride (c. friedel and j.m. crafts, _ann. chim. phys._, 1888 (6) 14, p. 435); by heating phenol carboxylic acids with baryta; and, in small quantities by the oxidation of benzene with hydrogen peroxide or nascent ozone (a.r. leeds, _ber._, 1881, 14, p. 976). it crystallizes in rhombic needles, which melt at 42.5-43 deg. c., and boil at 182-183 deg. c.; its specific gravity is 1.0906 (0 deg. c.). it has a characteristic smell, and a biting taste; it is poisonous, and acts as a powerful antiseptic. it dissolves in water, 15 parts of water dissolving about one part of phenol at 16-17 deg. c., but it is miscible in all proportions at about 70 deg. c.; it is volatile in steam, and is readily soluble in alcohol, ether, benzene, carbon bisulphide, chloroform and glacial acetic acid. it is also readily soluble in solutions of the caustic alkalis, slightly soluble in aqueous ammonia solution, and almost insoluble in sodium carbonate solution. when exposed in the moist condition to the air it gradually acquires a red colour. with ferric chloride it gives a violet coloration, and with bromine water a white precipitate of tribrom-phenol. when phenol is passed through a red-hot tube a complex decomposition takes place, resulting in the formation of benzene, toluene, naphthalene, &c. (j.g. kramers, _ann._, 1877, 189, p. 129). chromium oxychloride reacts violently on phenol, producing hydroquinone ether, o(c6h4oh)2; chromic acid gives phenoquinone, and potassium permanganate gives paradiphenol, oxalic acid, and some salicylic acid (r. henriques, _ber._, 1888, 21, p. 1620). in alkaline solution, potassium permanganate oxidizes it to inactive tartaric acid and carbon dioxide (o. doebner, _ber._, 1891, 24, p. 1755). when distilled over lead oxide, it forms diphenylene oxide, (c6h4)2o; and when heated with oxalic acid and concentrated sulphuric acid, it forms aurin, c19h14o3. it condenses with aceto-acetic ester, in the presence of sulphuric acid, to [beta]-methyl coumarin (h. v. pechmann and j.b. cohen, _ber_., 1884, 17, p. 2188). the hydrogen of the hydroxyl group in phenol can be replaced by metals, by alkyl groups and by acid radicals. the metallic derivatives (phenolates, phenates or carbolates) of the alkali metals are obtained by dissolving phenol in a solution of a caustic alkali, in the absence of air. potassium phenolate, c6h5ok, crystallizes in fine needles, is very hygroscopic and oxidizes rapidly on exposure. other phenolates may be obtained from potassium phenolate by precipitation. the alkyl derivatives may be obtained by heating phenol with one molecular proportion of a caustic alkali and of an alkyl iodide. they are compounds which greatly resemble the mixed ethers of the aliphatic series. they are not decomposed by boiling alkalis, but on heating with hydriodic acid they split into their components. _anisol_, phenyl methyl ether, c6h5.o.ch3, is prepared either by the above method or by the action of diazo-methane on phenol, c6h5oh+ch2n2 = n2+c6h5.o.ch3 (h. v. pechmann, _ber_., 1895, 28, p. 857); by distilling anisic acid (para-methoxy benzoic acid) with baryta or by boiling phenyl diazonium chloride with methyl alcohol. it is a colourless pleasant-smelling liquid which boils at 154.3 deg. c. _phenetol_, phenyl ethyl ether, c6h5.o.c2h5, a liquid boiling at 172 deg. c., may be obtained by similar methods. a. hantzsch (_ber._, 1901, 34, p. 3337) has shown that in the action of alcohols on diazonium salts an increase in the molecular weight of the alcohol and an accumulation of negative groups in the aromatic nucleus lead to a diminution in the yield of the ether produced and to the production of a secondary reaction, resulting in the formation of a certain amount of an aromatic hydrocarbon. the acid esters of phenol are best obtained by the action of acid chlorides or anhydrides on phenol or its sodium or potassium salt, or by digesting phenol with an acid in the presence of phosphorus oxychloride (f. rasinski, _jour. f. prak. chem._, 1882 [2], 26, p. 62). phenyl acetate, c6h5.o.coch3, a colourless liquid of boiling point 193 deg. c., may be prepared by heating phenol with acetamide. when heated with aniline it yields phenol and acetanilide. phenyl benzoate, c6h5.o.coc5h5, prepared from phenol and benzoyl chloride, crystallizes in monoclinic prisms, which melt at 68-69 deg. c. and boil at 314 deg. c. phenol is characterized by the readiness with which it forms substitution products; chlorine and bromine, for example, react readily with phenol, forming ortho- and para- chlor- and -bromphenol, and, by further action, trichlor- and tribrom-phenol. iodphenol is obtained by the action of iodine and iodic acid on phenol dissolved in a dilute solution of caustic potash. nitro-phenols are readily obtained by the action of nitric acid on phenol. by the action of dilute nitric acid, ortho- and para-nitrophenols are obtained, the ortho-compound being separated from the para-compound by distillation in a current of steam. ortho-nitrophenol, c6h4.oh.no2(1.2), crystallizes in yellow needles which melt at 45 deg. c. and boil at 214 deg.c. para-nitrophenol, c6h4.oh.no2(1.4), crystallizes in long colourless needles which melt at 114 deg.c. meta-nitrophenol, c6h4.oh.no2.(1.3), is prepared from meta-nitraniline by diazotizing the base and boiling the resulting diazonium salt with water. by nitrating phenol with concentrated nitric acid, no care being taken to keep the temperature of reaction down, trinitrophenol (picric acid) is obtained (see picric acid). by the reduction of nitro-phenols, the corresponding aminophenols are obtained, and of these, the meta- and para-derivatives are the most important. para-aminophenol, c6h4.oh.nh2(1.4) melts at 148 deg. c., with decomposition. its most important derivative is phenacetin. meta-aminophenol, c6h4.oh.nh2(1.3), and dimethyl meta-aminophenol, c6h4.oh.n(ch3)2(1.3), are extensively employed in the manufacture of the important dyestuffs known as the rhodamines. the aminophenols also find application as developers in photography, the more important of these developers being amidol, the hydrochloride of diaminophenol, ortol, the hydrochloride of para-methylaminophenol, c6h4.oh.nhch3.hcl(1.4), rodinal, para-aminophenol, and metol, the sulphate of a methylaminophenol sulphonic acid. meta-aminophenol is prepared by reducing meta-nitrophenol, or by heating resorcin with ammonium chloride and ammonia to 200 deg. c. dimethyl-meta-aminophenol is prepared by heating meta-aminophenol with methyl alcohol and hydrochloric acid in an autoclave; by sulphonation of dimethylaniline, the sulphonic acid formed being finally fused with potash; or by nitrating dimethylaniline, in the presence of sulphuric, acid at 0 deg. c. in the latter case a mixture of nitro-compounds is obtained which can be separated by the addition of sodium carbonate. the meta-nitro-compound, which is precipitated last, is then reduced, and the amino group so formed is replaced by the hydroxyl group by means of the sandmeyer reaction. dimethyl-meta-aminophenol crystallizes in small prisms which melt at 87 deg. c. it condenses with phthalic anhydride to form rhodamine, and with succinic anhydride to rhodamine s. phenol dissolves readily in concentrated sulphuric acid, a mixture of phenol-ortho- and -para-sulphonic acids being formed. these acids may be separated by conversion into their potassium salts, which are then fractionally crystallized, the potassium salt of the para-acid separating first. the ortho-acid, in the form of its aqueous solution, is sometimes used as an antiseptic, under the name of aseptol. a _thiophenol_, c6h5sh, is known, and is prepared by the action of phosphorus pentasulphide on phenol, or by distilling a mixture of sodium benzene sulphonate and potassium sulphydrate. it is a colourless liquid, which possesses a very disagreeable smell, and boils at 168 deg. c. various methods have been devised for the quantitative determination of phenol. j. messinger and g. vortmann (_ber._, 1890, 23, p. 2753) dissolve phenol in caustic alkali, make the solution up to known volume, take an aliquot part, warm it to 60 deg. c., and add decinormal iodine solution until the liquid is of a deep yellow colour. the mixture is then cooled, acidified by means of sulphuric acid, and titrated with decinormal sodium thiosulphate solution. s.b. schryver (_jour, of soc. chem. industry_, 1899, 18, p. 553) adds excess of sodamide to a solution of the phenol in a suitable solvent, absorbs the liberated ammonia in an excess of acid, and titrates the excess of acid. see also c.e. smith, _amer. jour. pharm._, 1898, 369. _pharmacology and therapeutics_.--carbolic acid is an efficient parasiticide, and is largely used in destroying the fungus of ringworm and of the skin disease known as _pityriasis versicolor_. when a solution of the strength of about 1 in 20 is applied to the skin it produces a local anaesthesia which lasts for many hours. if concentrated, however, it acts as a caustic. it never produces vesication. the drug is absorbed through the unbroken skin--a very valuable property in the treatment of such conditions as an incipient whitlow. a piece of cotton wool soaked in strong carbolic acid will relieve the pain of dental caries, but is useless in other forms of toothache. taken internally, in doses of from one to three grains, carbolic acid will often relieve obstinate cases of vomiting and has some value as a gastric antiseptic. _toxicology_.--carbolic acid is distinguished from all other acids so-called--except oxalic acid and hydrocyanic acid--in that it is a neurotic poison, having a marked action directly upon the nervous system. in all cases of carbolic acid poisoning the nervous influence is seen. if it be absorbed from a surgical dressing there are no irritant symptoms, but when the acid is swallowed in concentrated form, symptoms of gastro-intestinal irritation occur. the patient becomes collapsed, and the skin is cold and clammy. the breathing becomes shallow, the drug killing, like nearly all neurotic poisons (alcohol, morphia, prussic acid, &c.), by paralysis of the respiratory centre, and the patient dying in a state of coma. the condition of the urine is of the utmost importance, as it is often a clue to the diagnosis, and in surgical cases may be the first warning that absorption is occurring to an undue degree. the urine becomes dark green in colour owing to the formation of various oxidation products such as pyrocatechin. fifteen grains constitute an exceedingly dangerous dose for an adult male of average weight. other symptoms of undue absorption are vertigo, deafness, sounds in the ears, stupefaction, a subnormal temperature, nausea, vomiting and a weak pulse (sir thomas fraser). the antidote in cases of carbolic acid poisoning is any soluble sulphate. carbolic acid and sulphates combine in the blood to form sulpho-carbolates, which are innocuous. the symptoms of nerve-poisoning are due to the carbolic acid (or its salts) which circulate in the blood after all the sulphates in the blood have been used up in the formation of sulpho-carbolates (hence, during administration of carbolic acid, the urine should frequently be tested for the presence of free sulphates; as long as these occur in the urine, they are present in the blood and there is no danger). the treatment is therefore to administer an ounce of sodium sulphate in water by the mouth, or to inject a similar quantity of the salt in solution directly into a vein or into the subcutaneous tissues. magnesium sulphate may be given by the mouth, but is poisonous if injected intravenously. if the acid has been swallowed, wash out the stomach and give chalk, the carbolate of calcium being insoluble. alkalis which form soluble carbolates are useless. give ether and brandy subcutaneously and apply hot water-bottles and blankets if there are signs of collapse. carbon (symbol c, atomic weight 12), one of the chemical non-metallic elements. it is found native as the diamond (q.v.), graphite (q.v.), as a constituent of all animal and vegetable tissues and of coal and petroleum. it also enters (as carbonates) into the composition of many minerals, such as chalk, dolomite, calcite, witherite, calamine and spathic iron ore. in combination with oxygen (as carbon dioxide) it is also found to a small extent in the atmosphere. it is a solid substance which occurs in several modifications, differing very much in their physical properties. _amorphous carbon_ is obtained by the destructive distillation of many carbon compounds, the various kinds differing very greatly as regards physical characters and purity, according to the substance used for their preparation. the most common varieties met with are lampblack, gas carbon, wood charcoal, animal charcoal and coke. _lampblack_ is prepared by burning tar, resin, turpentine and other substances rich in carbon, with a limited supply of air; the products of combustion being conducted into condensing chambers in which cloths are suspended, on which the carbon collects. it is further purified by heating in closed vessels, but even then it still contains a certain amount of mineral matter and more or less hydrocarbons. it is used in the manufacture of printer's ink, in the preparation of black paint and in calico printing. _gas carbon_ is produced by the destructive distillation of coal in the manufacture of illuminating gas (see gas: _manufacture_), being probably formed by the decomposition of gaseous hydrocarbons. it is a very dense form of carbon, and is a good conductor of heat and electricity. it is used in the manufacture of carbon rods for arc lights, and for the negative element in the bunsen battery. _charcoal_ is a porous form of carbon; several varieties exist. _sugar charcoal_ is obtained by the carbonization of sugar. it is purified by boiling with acids, to remove any mineral matter, and is then ignited for a long time in a current of chlorine in order to remove the last traces of hydrogen. _animal charcoal_ (bone black) is prepared by charring bones in iron retorts. it is a very impure form of carbon, containing on the average about 80% of calcium phosphate. it possesses a much greater decolorizing and absorbing power than wood charcoal. a variety of animal charcoal is sometimes prepared by calcining fresh blood with potassium carbonate in large cylinders, the mass being purified by boiling out with dilute hydrochloric acid and subsequent reheating. _wood charcoal_ is a hard and brittle black substance, which retains the external structure of the wood from which it is made. it is prepared (where wood is plentiful) by stacking the wood in heaps, which are covered with earth or with brushwood and turf, and then burning the heap slowly in a limited supply of air. the combustion of the wood is conducted from the top downwards, and from the exterior towards the centre; great care has to be taken that the process is carried out slowly. the disadvantage in this process is that the by-products, such as pyroligneous acid, acetone, wood spirit, &c., are lost; as an alternative method, wood is frequently carbonized in ovens or retorts and the volatile products are condensed and utilized. charcoal varies considerably in its properties, depending upon the particular variety of wood from which it is prepared, and also upon the process used in its manufacture. it can be made at a temperature as low as 300 deg. c., and is then a soft, very friable material possessing a low ignition point. when made at higher temperatures it is much more dense, and its ignition point is considerably higher. charcoal burns when heated in air, usually without the formation of flame, although a flame is apparent if the temperature be raised. it is characterized by its power of absorbing gases; thus, according to j. hunter [_phil. mag._, 1863 (4), 25, p. 363], one volume of charcoal absorbs (at 0 deg. c. and 760 mm. pressure) 171.7 ccs. of ammonia, 86.3 ccs. of nitrous oxide, 67.7 ccs. of carbon monoxide, 21.2 ccs. of carbon dioxide, 17.9 ccs. of oxygen, 15.2 ccs. of nitrogen, and 4.4 ccs. of hydrogen [see also j. dewar, _ann. chim. phys._, 1904 (8), 3, p. 5]. it also has the power of absorbing colouring matters from solution. charcoal is used as a fuel and as a reducing agent in metallurgical processes. the element carbon unites directly with hydrogen to form acetylene when an electric arc is passed between carbon poles in an atmosphere of hydrogen (m. berthelot); it also unites directly with fluorine, producing, chiefly, carbon tetrafluoride cf4. it burns when heated in an atmosphere of oxygen, forming carbon dioxide, and when heated in sulphur vapour it forms carbon bisulphide (q.v.). when heated with nitrogenous substances, in the presence of carbonated or caustic alkali, it forms cyanides. it combines directly with silicon, at the temperature of the electric furnace, yielding _carborundum_, sic; and h. moissan has also shown that it will combine with many metals at the temperature of the electric furnace, to form carbides (q.v.). the specific heat of carbon varies with the temperature the following values having been obtained by h.f. weber (_jahresberichte_, 1874, p. 63):-- +-----------------+-----------------+-------------------+ | diamond. | graphite. |porous wood carbon.| +-------+---------+-------+---------+--------+----------+ | t deg.| sp. ht. | t deg.| sp. ht. | t deg. | sp. ht. | +-------+---------+-------+---------+--------+----------+ | -50.5 | 0.0635 | -50.3 | 0.1138 | 0-23 | 0.1653 | | -10.6 | 0.0955 | -10.7 | 0.1437 | 0-99 | 0.1935 | | +10.7 | 0.1128 | +10.8 | 0.1604 | 0-223 | 0-2385 | | 85.5 | 0.1765 | 61.3 | 0.1990 | | | | 206.1 | 0.2733 | 201.6 | 0.2966 | | | | 606.7 | 0.4408 | 641.9 | 0.4454 | | | | 985.0 | 0.4589 | 977.0 | 0.4670 | | | +-------+---------+-------+---------+--------+----------+ the atomic weight of carbon has been determined by j.b.a. dumas and by j.s. stas [_ann. chim. phys._, 1841 (3), 1, p. 1: _jahresb._, 1849, 223] by estimating the amount of carbon dioxide formed on burning graphite or diamond in a current of oxygen, the value obtained being 12.0 (o = 16). confirmatory evidence has also been obtained by o.l. erdmann and r.f. marchand (_jour. prak. chem._, 1841, 23, p. 159; see also f.w. clarke, _jahresb._, 1881, p. 7). _compounds_.--three oxides of carbon are known, namely, carbon suboxide, c3o2, carbon monoxide, co, and carbon dioxide, co2. _carbon suboxide_, c3o2, is formed by the action of phosphorus pentoxide on ethyl malonate (o. diels and b. wolf, _ber._, 1906, 39, p. 689), ch2(cooc2h5)2 = 2c2h4 + 2h2o + c3o2. at ordinary temperatures it is a colourless gas, possessing a penetrating and suffocating smell. it liquefies at 7 deg. c. it is an exceedingly reactive compound, combining with water to form malonic acid, with hydrogen chloride to form malonyl chloride, and with ammonia to form malonamide. when kept for some time in sealed tubes it changes to a yellowish liquid, from which a yellow flocculent substance gradually separates, and finally it suddenly solidifies to a dark red mass, which appears to be a polymeric form. its vapour density agrees with the molecular formula c3o2, and this formula is also confirmed by exploding the gas with oxygen and measuring the amount of carbon dioxide produced (see ketenes). _carbon monoxide_, co, is found to some extent in volcanic gases. it was first prepared in 1776 by j.m.f. lassone (_mem. acad. paris_) by heating zinc oxide with carbon, and was for some time considered to be identical with hydrogen. cruikshank concluded that it was an oxide of carbon, a fact which was confirmed by clement and j.b. desormes (_ann. chim. phys._, 1801, 38, p. 285). it may be prepared by passing carbon dioxide over red-hot carbon, or red-hot iron; by heating carbonates (magnesite, chalk, &c.) with zinc dust or iron; or by heating many metallic oxides with carbon. it may also be prepared by heating formic and oxalic acids (or their salts) with concentrated sulphuric acid (in the case of oxalic acid, an equal volume of carbon dioxide is produced); and by heating potassium ferrocyanide with a large excess of concentrated sulphuric acid, k4fe(cn)6 + 6h2so4 + 6h2o = 2k2so4 + feso4 + 3(nh4)2so4 + 6co. it is a colourless, odourless gas of specific gravity 0.967 (air = 1). it is one of the most difficultly liquefiable gases, its critical temperature being -139.5 deg. c., and its critical pressure 35.5 atmos. the liquid boils at -190 deg. c., and solidifies at -211 deg.c. (l.p. cailletet, _comptes rendus_, 1884, 99, p. 706). it is only very slightly soluble in water. it burns with a characteristic pale blue flame to form carbon dioxide. it is very poisonous, uniting with the haemoglobin of the blood to form carbonyl-haemoglobin. it is a powerful reducing agent, especially at high temperatures. it is rapidly absorbed by an ammoniacal or acid (hydrochloric acid) solution of cuprous chloride. it unites directly with chlorine, forming carbonyl chloride or phosgene (see below), and with nickel and iron to form nickel and iron carbonyls (see nickel and iron). it also combines directly with potassium hydride to form potassium formate (see formic acid). the volume composition of carbon monoxide is established by exploding a mixture of the gas with oxygen, two volumes of the gas combining with one volume of oxygen to form two volumes of carbon dioxide. this fact, coupled with the determination of the vapour density of the gas, establishes the molecular formula co. _carbon dioxide_, co2, is a gas first distinguished from air by van helmont (1577-1644), who observed that it was formed in fermentation processes and during combustion, and gave to it the name _gas sylvestre_. j. black (_edin. phys. and lit. essays_, 1755) showed that it was a constituent of the carbonated alkalis and called it \"fixed air.\" t.o. bergman, in 1774, pointed out its acid character, and a.l. lavoisier (1781-1788) first proved it to be an oxide of carbon by burning carbon in the oxygen obtained from the decomposition of mercuric oxide. it is a regular constituent of the atmosphere, and is found in many spring waters and in volcanic gases; it also occurs in the uncombined condition at the grotto del cane (naples) and in the poison valley (java). it is a constituent of the minerals cerussite, malachite, azurite, spathic iron ore, calamine, strontianite, witherite, calcite aragonite, limestone, &c. it may be prepared by burning carbon in excess of air or oxygen, by the direct decomposition of many carbonates by heat, and by the decomposition of carbonates with mineral acids, m2co8 + 2hcl = 2mcl + h2o + co2. it is also formed in ordinary fermentation processes, in the combustion of all carbon compounds (oil, gas, candles, coal, &c.), and in the process of respiration. it is a colourless gas, possessing a faint pungent smell and a slightly acid taste. it does not burn, and does not support ordinary combustion, but the alkali metals and magnesium, if strongly heated, will continue to burn in the gas with formation of oxides and liberation of carbon. its specific gravity is 1.529 (air = 1). it is readily condensed, passing into the liquid condition at 0 deg. c. under a pressure of 35 atmospheres. its critical temperature is 31.35 deg. c., and its critical pressure is 72.9 atmos. the liquid boils at -78.2 deg. c. (l atmo.), and by rapid evaporation can be made to solidify to a snow-white solid which melts at -65 deg. c.(see liquid gases). carbon dioxide is moderately soluble in water, its coefficient of solubility at 0 deg. c. being 1.7977 (r. bunsen). it is still more soluble in alcohol. the solution of the gas in water shows a faintly acid reaction and is supposed to contain _carbonic acid_, h2co3. the gas is rapidly absorbed by solutions of the caustic alkalis, with the production of alkaline carbonates (q.v.), and it combines readily with potassium hydride to form potassium formate. it unites directly with ammonia gas to form ammonium carbamate, nh2coonh4. it may be readily recognized by the white precipitate which it forms when passed through lime or baryta water. carbon dioxide dissociates, when strongly heated, into carbon monoxide and oxygen, the reaction being a balanced action; the extent of dissociation for varying temperatures and pressures has been calculated by h. le chateller (_zeit. phys. chem._, 1888, 2, p. 782; see h. sainte-claire deville, _comptes rendus_, 1863, 56, p. 195 et seq.). the volume composition of carbon dioxide is determined by burning carbon in oxygen, when it is found that the volume of carbon dioxide formed is the same as that of the oxygen required for its production, hence carbon dioxide contains its own volume of oxygen. carbon dioxide finds industrial application in the preparation of soda by the solvay process, in the sugar industry, in the manufacture of mineral waters, and in the artificial production of ice. _carbonyl chloride_ (phosgene), cocl2, was first obtained by john davy (_phil. trans._, 1812, 40, p. 220). it may be prepared by the direct union of carbon monoxide and chlorine in sunlight (th. wilm and g. wischin, _ann_., 1868, 14, p. 150); by the action of phosphorus pentoxide on carbon tetrachloride at 200-210 deg. c. (g. gustavson, _ber_., 1872, 5, p. 30), 4ccl4 + p4o10 = 2co2 + 4pocl3 + 2cocl2; by the oxidation of chloroform with chromic acid mixture (a. emmerling and b. lengyel, _ber_., 1869, 2, p. 54), 4chcl3 + 3o2 = 4cocl2 + 2h2o + 2cl2; or most conveniently by heating carbon tetrachloride with fuming sulphuric acid (h. erdmann, _ber_., 1893, 26, p. 1993), 2so3 + ccl4 = s2o5cl2 + cocl2. it is a colourless gas, possessing an unpleasant pungent smell. its vapour density is 3.46 (air = 1). it may be condensed to a liquid, which boils at 8 deg. c. it is readily soluble in benzene, glacial acetic acid, and in many hydrocarbons. water decomposes it violently, with formation of carbon dioxide and hydrochloric acid. it reacts with alcohol to form chlorcarbonic ester and ultimately diethyl carbonate (see carbonates), and with ammonia it yields urea (q.v.). it is employed commercially in the production of colouring matters (see benzophenone), and for various synthetic processes. _carbon oxysulphide_, cos, was first prepared by c. than in 1867 (_ann. suppl._, 5, p. 236) by passing carbon monoxide and sulphur vapour through a tube at a moderate heat. it is also formed by the action of sulphuretted hydrogen on the isocyanic esters, 2conc2h5 + h2s = cos + co(nhc2h5)2, by the action of concentrated sulphuric acid on the isothiocyanic esters, rncs + h2o = cos + rnh2, or of dilute sulphuric acid on the thiocyanates. in the latter reaction various other compounds, such as carbon dioxide, carbon bisulphide and hydrocyanic acid, are produced. they are removed by passing the vapours in succession through concentrated solutions of the caustic alkalis, concentrated sulphuric acid, and triethyl phosphine; the residual gas is then purified by liquefaction (w. hempel, _zeit. angew. chemie_, 1901, 14, p. 865). it is also formed when sulphur trioxide reacts with carbon bisulphide at 100 deg. c., cs2 + 3so3 = cos + 4so2, and by the decomposition of ethyl potassium thiocarbonate with hydrochloric acid, co(oc2h5)sk + hcl = cos + kcl + c2h5oh. it is a colourless, odourless gas, which burns with a blue flame and is decomposed by heat. its vapour density is 2.1046 (air = 1). the liquefied gas boils at -47 deg. c. under atmospheric pressure. it is soluble in water; the aqueous solution gradually decomposes on standing, forming carbon dioxide and sulphuretted hydrogen. it is easily soluble in solutions of the caustic alkalis, provided they are not too concentrated, forming solutions of alkaline carbonates and sulphides, cos + 4kho = k2co3 + k2s + 2h2o.",
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