262 M. Bmsy on Sulphuric Acid. [Oct, 



blue : the same effect is produced by the addition of common 

 sulphuric acid ; the liquid, however, always retains a sensible 

 tint of red, especially when seen by transmitted light. 



Of the Maimer of obtaining the Fuming Acid of Saxony. 



"We have seen that the Nordhausen acid differs from the 

 common by containing a larger proportion of real acid, and that 

 the anhydrous acid may be obtained by the distillation of dry 

 fulphate of iron ; consequently we may obtain the acid of every 

 degree of strength, by properly receiving the products of that 

 distillation." 



By distilling persulphate of iron, in the manner already de- 

 scribed, and receiving the product in distilled water, an acid was 

 obtained, which marked 20° of Beaume's areometer (= specific 

 gravity of about 1-167). By frequent repetitions of the process, 

 and always condensing the vapours in the same liquid, an 

 exceedingly fuming acid was obtained, similar to that from 

 Nordhausen in al! respects, except in colour. But the most 

 economical method of preparing the Nordhausen acid is to 

 receive the product of the distillation of sulphate of iron in com- 

 mon sulphuric acid of the specific gravity of 1*844. 



But in operating on a large scale, a difficulty occurs when we 

 attempt to pass the vapours into common sulphuric acid, from 

 their corrosive action, assisted by the necessary pressure, on the 

 lutes and joinings of the apparatus ; for if pressure be not 

 employed, a large portion of the sulphuric acid is carried off by 

 the sulphurous acid and oxygen gases, which are disengaged at 

 the same time, but not condensed. 



" To obviate this inconvenience as far as possible, the appa- 

 ratus should be so constructed that the vapours may be disen- 

 gaged through a narrow orifice, and their points of contact with 

 the acid multiplied. For this purpose, I use a retort with an 

 adopter, the end of which is slightly drawn out; to this 1 adapt 

 a quilled receiver, and to that a tubulated one. The acid to be 

 saturated is put into these receivers. Operating in this way, 20 

 parts of desiccated sulphate of iron converted 7*5 parts of com- 

 mon, into 10 parts of very fuming sulphuric acid. 



" When a large excess of sulphuric vapours are passed into 

 common acid, in order to have it as concentrated as possible, it 

 is obtained crystallized at common temperatures in fine, transpa- 

 rent, very fuming crystals. It is difficult to ascertain their speci- 

 fic gravity, but i found that of the supernatant liquid to be 

 •1*9U7, which, I believe, is less than it would be if it were per- 

 fectly free from a portion of sulphurous acid. 



* I placed common sulphuric acid, specific gravity 1*845, in 

 a flask, and poured over it liquid, anhydrous sulphurous acid, 

 and slightly agitated the two liquids ; a portion of the sulphurous 

 arid dissolved, and the rest remained on the surface, without 



