Researches on the Sulphuric Acid ofNordhausen. 147 



from this that decomposition to a smaller extent would take 

 place if persulphate of iron were used; and, on trying the experi- 

 ment the sulphurous acid and oxygen came over from the first in 

 the proportions of 2 and 1, and the sulphuric acid condensed in 

 the water. 



To ascertain whether the water had any influence \n forming 

 sulphuric acid from the vapours, it was now removed, and in its 

 place was put a small dry flask, cooled by a mixture of ice and 

 salt. The distillation was made as before, oxygen came over 

 during the whole time, but scarcely any sulphurous acid, and very 

 fevf white vapours. When the apparatus was taken down, a 

 colourless transparent liquid was found in the matrass, emitting 

 abundance of white vapours, which exposed to the air partly eva- 

 porated; and the rest formed crystals, at first opaque, then becoming 

 transparent, and finally a liquid, or common sulphuric acid. When 

 the liquid was left in an open vessel to which the air had not 

 free access it sublimed, resembling benzoic acid in appearance ; 

 put to water it caused explosions, liberating sulphurous acid gas, 

 and giving solution of sulphuric acid; concentrated sulphuric acid 

 caused the evolution of sulphurous acid, but added cautiously in 

 small quantities, transparent crystals were obtained. Finally, on 

 passing this acid over baryta, sulphate ai)d sulphuret of baryta 

 were formed. 



At first hyposulphuric acid was suspected, but it was soon found 

 that the liquid was a mere mixture of sulphuric and sulphurous 

 acid : when it was distilled it boiled at about 25° Fahr. for a short 

 time, but it was soon requisite to raise the temperature ; and the 

 portion which first came oflPwhen condensed was found to be pure 

 liquid sulphurous acid, whilst what remained in the retort crystal- 

 lized, and proved to be anhydrous sulphuric acid. To put this 

 conclusion beyond doubt, it was only necessary to ascertain 

 whether sulphurous acid gas alone would condense by cold, and 

 this was found to be the case*. 



Alum and all the sulphates decomposable by heat gave similar 

 results. When the salts are not quite dry less liquid is obtained, 

 and crystals of an hydrated acid are formed in the neck of the 

 retort; but it is always easy to obtain a product free from water, 

 by letting the first portions of the produce pass away ; and 

 indeed, the receiver should never be adopted before the white suf- 

 focating vapours pass in great abundance. 



The instantaneous solution of indigo by the fuming acid obtained 

 from the sulphates is a very remarkable property ; but the solution 

 obtained, unlike that made with the common sulphuric acid, is of a 



• Sec our last Numbnr, p. 391. M. Bussy's experiment is a remarkable 

 confirmation of what Mongc and Clouet did, even almost to the degree they 

 mention. Sec QuarleHy Journal, XVI. p. 234. 



L2 



