1824.J M. Bussi/ on Sulphuric Acid. 263 



mixing with the sulphuric acid ; but by continuing the agitation 

 a portion of the sulphurous acid was interfused amongst the 

 sulphuric, and gave it that sort of opacity which oil imparts to 

 water. By repose, the acids separated again, the sulphuric 

 subsiding and resuming its transparency. After the operation, 

 the sulphuric acid had a strong odour of sulphurous acid ; its 

 specific gravity was diminished, and it exhaled no white 

 vapours." 



The density of the Nordhausen acid should exceed that of 

 66° of Beaume's hydrometer (= specific gravity 1-848), itshould 

 be as high as 68° (= about specific gravity 1-900). 



" Although the fuming sulphuric acid be not much employed, 

 it would probably come into more frequent use if it could be 

 obtained at a lower price ; for it possesses very valuable proper- 

 ties, especially to the manufacturer of dyed cloths, and to dyers 

 in general ; since it dissolves a much larger quantity of indigo 

 than the common acid, and is very superior in regard to its 

 acidity ; and, as in many cases, this acid solution of indigo 

 cannot be employed on account of its action on the cioth, or the 

 other colours, it is converted into acetate of indigo by precipitat- 

 ing the sulphuric acid by means of acetate of lead. It is 

 obvious, therefore, that it must be extremely advantageous to 

 dissolve the greatest possible quantity of indigo in a given quan- 

 tity of acid." 



" It results from what has been stated above, 



" 1. That the fuming sulphuric acid of Nordhausen is merely 

 common acid, containing a certain quantity of anhydrous acid, 

 to which it owes its characteristic properties ; that the sulphur- 

 ous acid is only an accidental ingredient, and does not essen- 

 tially affect its properties. 



" 2. That the anhydrous acid may be separated by distilla- 

 tion, and that it possesses, amongst other remarkable proper- 

 ties, that of forming a red solution of indigo. 



" 3. That all the sulphates, decomposable by heat, give off 

 oxygen, sulphurous acid and sulphuric acid, which is essentially 

 characterized by the white vapours that are produced during the 

 decomposition. 



" 4. That all those sulphates may be used in preparing both 

 the common and the fuming sulphuric acid, by means of the 

 process which has been described above." 



