SULPHURIC ACID AND SULPHUR COMPOUNDS. 631 



combined as salts, being excreted per diem. Two forms of salts exist 

 (1) the ordinary and strictly inorganic sulphates of the form M' 2 S0 4 , 

 and (2) the so-called conjugated or ethereal sulphates, which contain 

 organic radicles; the composition of these will be clear from what 

 follows. 



If ordinary alcohol be boiled with its own bulk of strong sulphuric 

 acid, under a vertical condenser, a crystalline product is formed which 

 is known as ethylhydrogen sulphate, or sulphovinic acid. The com- 

 position of this is explained by the following equation : 



C 2 H r .OH H0. H 2 C 2 H 5 O v 



+ >S0 2 = + >S0 2 



H / H / 



(alcohol) (sulphuric acid) (water) (ethylhydrogen sulphate) 



By elimination of water, the ethyl radicle (C 2 H 5 - ) becomes " con- 

 jugated " with the sulphuric acid, and a monovalent acid is formed, 

 which yields salts of the type M'C. 2 H 5 : S0 4 . On boiling such salts 

 with hydrochloric acid, the sulphovinic acid is first liberated, and then, 

 by absorption of water, splits up once more into alcohol and sulphuric 

 acid. 



The " conjugated sulphates " of the urine are precisely analogous 

 salts, which undergo like decomposition when boiled with HC1. But, 

 instead of ethyl, the radicles conjugated with the sulphuric acid are 

 nearly always derived from aromatic precursors. In fact, as we have 

 already seen, most of the aromatic compounds of the urine described on 

 p. 605 et seq. are present as conjugated sulphates ; and the proportion of 

 the sulphuric acid present in this form depends upon the factors which 

 increase or decrease these aromatic substances. The chief salts present, 

 therefore, under ordinary circumstances, are those of kresyl- indoxyl- 

 and skatoxyl-sulphuric acids. 



Normally, the sulphuric acid so combined amounts to about one- 

 tenth of the whole ; nine-tenths being in the form of ordinary sulphates. 

 An increased proportion of ethereal sulphates is found when, for any 

 reason, there is increase of proteid putrefaction in the body, and especi- 

 ally in the bowel ; and also when larger amounts of aromatic compounds 

 than usual are taken by the mouth. In man they may be greatly in- 

 creased during starvation, whereas, according to I. Munk, they are absent 

 from the urine of a starving dog. 



For the detection and estimation of the sulphates we rely upon the forma- 

 tion of the insoluble barium salt. All the sulphuric acid originally present as 

 ordinary sulphates is precipitated as white crystalline barium sulphate, when a 

 soluble barium salt is added to the urine, previously made acid with acetic acid. 

 On the other hand, the barium salts of the conjugated sulphuric acids are soluble, 

 so that when the barium precipitate, obtained as above, is filtered off, the 

 ethereal sulphates still exist in the filtrate. But, as we have seen, they are 

 decomposed on boiling with hydrochloric acid, splitting up into sulphuric acid 

 and the hydrate of the conjugated radicle. It is evident, therefore, that if the 

 above-mentioned filtrate be so boiled with hydrochloric acid, a further precipi- 

 tate of barium sulphate may be obtained, the amount of which will be a 

 measure of the proportion of ethereal sulphates present. 



One-fifth of the total sulphur of the urine is present, not in any form 

 of sulphate, .but in less oxidised compounds. This fraction may be 

 spoken of as the "neutral sulphur" in contradistinction to the "acid 



