Mr.Buckton are«?Dv.Hofmann on the Conjugate Sulpha-acids. 281 



The process of conyerting sulphanilic acid into the disulpho-com- 

 pound is rather tedious. It may, however, be effected without fail, 

 by treating for several hours the perfectly dry crystalline acid, mixed 

 with strong Nordhausen acid, to the consistence of a paste. The 

 heat should not exceed that at which sulphurous acid just com- 

 mences to be evolved. We employed an air-bath heated from 160° 

 to 1 70° C, and the digestion was continued until a portion removed 

 by a glass rod showed no trace of crystallization when cooled or 

 moistened with water. 



Treatment with carbonate of barium yielded in this manner a very 

 soluble salt, which furnished a brittle gum when evaporated. The 

 new substance was precipitated from its solution by alcohol and 

 dried at 200° C. A determination of the barium and the sulphur 

 led to the expression C^^ (H^. Ba^) N S^ 0,3, 

 which is the formula of disulphauilate of barium. 



This salt is readily attacked by concentrated nitric acid with oxi- 

 dation of the sulphur. It blackens when strongly heated on pla- 

 tinum foil, and yields sulphurous acid without inflaming, a deport- 

 ment in which it differs from sulphanilate of barium, which burns 

 with a bright flame. When heated in close vessels it forms a ciy- 

 stalline sublimate, which consists of sulphite of aniline. 



Disulphanilic acid is prepared by decomposing the lead-salt with 

 hydrosulphuric acid. It is very soluble in water, and crystallizes 

 with difficulty. It may be precipitated from a strong .aqueous 

 solution by alcohol in the form of white grains. The precipitation 

 is assisted by the addition of a little ether. It has a very rough and 

 acid taste. 



We have also prepared the silver-salt by saturating the acid with 

 carbonate of silver. The most ready method of obtaining it in a 

 solid state is by precipitation with alcohol and ether. The aqueous 

 solution, by concentration, deposits a black powder which makes it 

 very difficult to obtain the crystals colourless. 



The formula of disulphauilate of silver is 

 C,,(Il5Ag2)NS,0,2. 



The potassa-salt is crystalline. It forms small grains or minute 

 needles, which are insoluble in alcohol. 



The researches detailed in the preceding paragraphs may serve to 

 characterize more fully a class of compounds of which only a few 

 terms, isolated and scattered in widely different groups, had been 

 previously observed. The only disulpho-acids hitherto known, are 

 Berzelius's and Laurent's disulj)houaphthalic acid, Magnus's ethionic 

 (disulphethylic) acid, and lastly, dithiobenzic acid, recently discovered 

 by M. Kilkenkamj). To these we now add five new acids, belonging 

 to several of the most important series of compounds: — 



Disuljihometholic acid C2 II4 S^ Oj^. 



Disulphetholic acid ^4^6 S4 0i2" 



Disulphopropiolic acid CyllgSjO,.,. 



Disulphobenzolic acid CjjIIfiSjOi.,. 



Disulphanilic acid Cj.^ II; N 840,2. 



