1824.] M. Bussy on Sulphuric Acid. 261 



" If the persulphate of iron be employed, sulphurous acid and 

 oxygen gases are obtained from the first, in the proportion of 

 two to one, and the white vapours, whose solution in water con- 

 stitutes sulphuric acid, are evolved at the same time." 



To ascertain if the sulphuric acid be disengaged as such from 

 the sulphate, or formed by its contact with the water, the same 

 apparatus was used, except that the water vessel was replaced 

 by a small perfectly dry matrass, immersed in a mixture of ice 

 and salt, and having a bent tube for the escape of the inconden- 

 sible gases. The heat was applied as before; oxygen gas was 

 given off during the whole process, but no sensible quantity of 

 sulphurous acid, and very few white vapours. After the opera- 

 tion, the matrass contained a colourless, transparent liquid, of 

 the specific gravity of T85 ; it gave off excessively abundant 

 white vapours, and by exposure to the air a portion of it evapo- 

 rated, and the rest crystallized. The crystals, which were at 

 first opaque, afterwards became transparent, and finished by 

 melting into liquid sulphuric acid. When left in an open vessel, 

 in which the air could not readily be renewed, it sublimed, and 

 crystallized like benzoic acid ; placed in contact with water it 

 produced strong explosions, sulphurous acid was disengaged, 

 and the liquid contained sulphuric acid ; the addition of concen- 

 trated sulphuric acid also occasions a great evolution of sulphur- 

 ous acid gas ; if the acid be cautiously added, and in small 

 quantity, transparent crystals are obtained ; lastly, when this 

 acid is passed in the state of vapour over previously heated caustic 

 barytes, it is converted into sulphate and sulphuret. 



" All these properties led me to suppose that this substance 

 might be hyposulphuric acid, which was converted by contact 

 with water or salifiable bases into sulphuric and sulphurous acid; 

 but I soon found that it is merely a mixture of those two. 

 Wheu distilled, and the product received in a cooling mixture, 

 the liquid boils at a temperature between 37° and 39° Fahr. If 

 the products be received separately, what comes over at first at 

 a low temperature is merely liquid sulphurous acid, scarcely 

 exhaling any white vapours, and wholly convertible into gas, at 

 common temperatures, with the peculiar odour of sulphurous 

 acid. If the distillation be .stopped when the first portion has 

 come over, the remainder crystallizes in small delicate needles, 

 and has all the characters of anhydrous sulphuric acid. Alum, 

 and the sulphates of copper, zinc, and antimony, and generally 

 all the sulphates decomposable by heat give, by similar treat- 

 ment, similar results." 



This fuming liquid dissolves indigo instantly without the 

 application of heat, and affords a magnificent purple solution, 

 precisely similar in colour to the vapour of indigo. When the 

 purple solution is exposed to the air, it attracts moisture, the 

 arid becomes common sulphuric acid, and the solution turns 



