Chap. I. Properties. cow.* Lassaigne examined the liquor contained in the allantois, and likewise that contained in the amnios of the cow, three several times in succession, and always found the acid in question in the liquor contained in the allantois, and never in the liquor amnii of the cow. He is of opinion that the liquid of the allantois had been given to Vauquelin and Buniva instead of the liquor of the amnios, and on that account changed the name from amniotic to allantoic acid.† Allantoic acid is obtained by evaporating the liquid of the allantois. It crystallizes in square prisms, its colour is white, and its lustre pearly. It is insipid, and not altered by exposure to the air. When heated it does not melt but blackens, is decomposed, and yields a great deal of carbonate of ammonia, some hydrocyanate of ammonia, and an oil, and it leaves a light charcoal, which burns away without leaving any residue. Water at the ordinary temperature of the atmosphere dissolves th part of its weight, and boiling water th of its weight of this acid. The solution reddens litmus paper; on cooling almost all the allantoic acid precipitates in fine needles. 30 It dissolves in boiling alcohol, but a portion crystallizes as the solution cools. The aqueous solution of this acid neither precipitates the solutions of lime, barytes, strontian, nor nitrate of silver, nitrate of mercury, acetate nor diacetate of lead. When treated with boiling nitric acid it is converted into a yellow gummy mass, which has an acid taste, but not the least bitterness. All the allantates are soluble in water and crystallizable. Allantate of barytes crystallizes in white prisms. Its taste is acid, and it is more soluble than allentate of potash. Its constituents, as determined by the analysis of Lassaigne, are This would make the atomic weight of this acid 63. The allantate of lead was found composed of This would make the atomic weight of this acid 58-33. The mean of these two results gives 60-66 for the atomic weight of this acid. Lassaigne subjected allantoic acid to analysis by means of oxide of copper, and obtained * Ann. de Chim. xxxiii. 279. † Ann. de Chim. et de Phys. xvii. 295. The atomic numbers agreeing with this analysis, and approach- Composition. ing nearest to the atomic weight deduced from the salts analyzed, are the following: 20 atoms oxygen 23 atoms carbon 9 atoms azote 72 atoms hydrogen This is of consequence the most complex acid which has hitherto been subjected to analysis. SECTION LI.OF HYDRO-CARBO-SULPHURIC ACID. Some steps towards the formation of this acid were made by History. Berzelius in his paper on bisulphuret of carbon, but it is to M. Zeise of Copenhagen that we are indebted for a full investigation of its nature." When an aqueous solution of ammonia and bisulphuret of carbon are left for a considerable time in contact with each other in a close vessel, a dark brownish-red liquid is formed, consisting of a mixture of hydro-carbo-sulphate of ammonia and sulpho-cyanate of ammonia, but containing no carbonate of ammonia. Bisulphuret of carbon dissolves very readily in an alcoholic solution of ammonia. The solution continues alkaline though a considerable excess of bisulphuret of carbon be added. It becomes speedily yellow, then brown, and smells of sulphuretted hydrogen. In about half an hour yellow feathershaped crystals of hydro-carbo-sulphate of ammonia are formed. These crystals are to be separated and dried by pressure between folds of blotting paper. Being now dissolved in water, and the solution mixed with dilute muriatic acid, an oily liquid separates, which is hydro-carbo-sulphuric acid. This acid is separated from the watery portion by means of a funnel. Hydro-carbo-sulphuric acid obtained by this process is a Properties, reddish brown transparent oily-looking liquid, heavier than * Schweigger's Jahrbuch, xi. 98, and 170. Chap. I. Composition. History. water, and having a peculiar smell mixed with that of sulphuretted hydrogen. M. Zeise is of opinion that this acid is a compound of hydrogen with a combination of sulphur and carbon in different proportions from what constitutes bisulphuret of carbon. To this compound he has given the name of xanthine, and he considers it as a compound of Its atomic weight therefore is 6-75, and it is in reality a tersulphate of carbon if Zeise's notion respecting its constitution be correct. This xanthine has the property of combining with the different bases in the same way as chlorine, bromine, iodine, and cyanogen, and to these compounds, several of which have been described by Zeise, he has given the name of xanthides. Hydro-carbo-sulphuric acid, or hydro-xanthic acid, as it is also called, is a compound, according to Zeise, of Hence the reason of the name. Or we may consider it as a compound of It is obvious that the atomic constitution of the acid, whichever view we take, will be the same. The first is conformable to the opinions formed by Zeise, but some of the changes which the acid undergoes rather favour the second. Nor are we to consider the constituents of the acid as perfectly established. For Zeise rather drew his deductions from theoretical views than from actual experiment. The salts which this acid forms, and several of which have been examined by Zeise, are called hydro-carbo-sulphates, or hydro-xanthates. SECTION LII.—OF SULPHO-VINIC ACID. It has been known for many years that when concentrated sulphuric acid and alcohol are mixed together in a retort, the mixture is accompanied by the evolution of much heat, and that when it is distilled a very volatile and inflammable liquid is obtained, distinguished by the name of sulphuric ether. Fourcroy and Vauquelin, in a paper on etherification, published in an early volume of the Annales de Chimie, endeavoured to prove that the sulphuric acid merely acted by abstracting a portion of the water, and that ether is alcohol deprived of a certain proportion of its water. This opinion was called in question by M. Dabit,* who endeavoured to prove that during the process the sulphuric acid undergoes decomposition, that it yields a portion of its oxygen to the alcohol, and that a new acid is formed, intermediate between sulphurous and sulphuric acid. Fourcroy and Vauquelin objected to this opinion of Dabit, that it was altogether unsupported by experiment, and could not therefore be adopted by chemists. Two years after, Dabit published a second memoir on the formation of ether, in which he demonstrates by very decisive experiments that a new acid is formed during the conversion of alcohol into ether, by the action of sulphuric acid. It is difficult to explain why no notice whatever was taken of this interesting paper of Dabit, and why no person thought it worth his while to repeat his experiments. The fact is, that ever since chemistry existed as a science, there has always been some individual, whose opinions for the time were adopted by the chemists on the continent without discussion or hesitation. Fourcroy at that time enjoyed that situation in France, and the experiments of Dabit were neglected and forgotten, because they were inconsistent with the opinions of that eloquent lecturer. Dabit prepared several salts containing his new acid as a constituent, and showed by the most decisive experiments that this new acid was neither sulphuric nor sulphurous, though it contained sulphur as an essential constituent. In the year 1818 Dr. Serturner of Einbeck, published an elaborate paper on the combination of acids with bases and in different substances.§ In this paper he affirms that sulphuric acid in acting on alcohol to form ether, produces no fewer than three acids, which he distinguishes by the names of acidum protonothionicum, acidum deutonothionicum, and acidum tritanothionicum. The first of these acids is obtained, he says, when equal weights of very strong alcohol and sulphuric acid are mixed together. This mixture is to be heated and then mixed with a sufficient quantity of chalk to saturate the acid which it Ann. de Chim. xxxiv. 289. + Ibid. p. 318. Class I Div. II, Chap. I. contains. The liquid being filtered and evaporated yields protonothionate of lime, from which the acid may be obtained by means of sulphuric acid. The second acid is obtained from the residue after the distillation of ether, by exactly a similar process; and the third acid is formed when the second acid is exposed to the air. It absorbs oxygen, and is converted into tritonothionic acid. Next year M. Vogel of Munich published a paper on the action of sulphuric acid on alcohol, with a demonstration of the formation of a new acid, to which he gave the name of sulphovinic.* This paper of Vogel was commented on at considerable length by Serturner, soon after its appearance.† Vogel mixed together equal parts of alcohol of the specific gravity 0·817 and concentrated sulphuric acid, and preserved the mixture for eight days in a stoppered bottle. He then divided the liquid into two equal parts, one of which was saturated with carbonate of barytes, and the other with carbonate of lead. The solutions being filtered and evaporated, yielded crystals of sulpho-vinate of barytes and sulpho-vinate of lead. He separated the sulpho-vinic acid from both of these salts, ascertained its characters, and determined the nature and properties of the sulpho-vinates. He pointed out the analogy between sulphovinic acid and hyposulphuric acid. But he did not subject any of the sulpho-vinates to an analysis. Soon after the appearance of Vogel's paper, an interesting account of the discovery of sulpho-vinic acid was published by Gay-Lussac, accompanied by some experiments of his own, from which he drew as a conclusion, that sulpho-vinic acid is hyposulphuric acid united with a certain quantity of vegetable matter.t In the year 1826, a very interesting set of experiments by Mr. Hennell was published on the mutual action of sulphuric acid and alcohol, with observations on the composition and properties of the resulting compound.§ In this paper, Mr. Hennell shows the nature of oil of wine, a liquid which is obtained in the process for making sulphuric ether. It is obtained by continuing the distillation after all ether ceases to come off. Mr. Hennell discovered that this oil of wine is a compound of * Gilbert's Annalen, Ixiii. 81. + Ibid. Ixiv. 67. |