{the Hydrate of) Sulphuric Acid with Nitric Oxide. 87 



combining with the sulphuric acid, while the latter is present 

 in great quantity in the mother-liquor. It is hence evident, 

 that the crystals formed in this manner are contaminated either 

 by nitric acid or by the nitrate of nitric oxide. 



I now prepared these crystals by passing sulphurous acid 

 and nitric oxide into a large vessel filled with atmospheric air, 

 into which, by means of a glass tube, I could spurt water or 

 blow air. With the presence of some water and an excess of 

 nitric oxide, the crystals formed immediately, and covered 

 partly the inner sides of the vessel, partly appeared in the 

 centre in crystalline flakes, quite similar to snow. Decom- 

 posed by water, nitric oxide was abundantly evolved; but if 

 this solution was boiled with sulphuric acid and water, and 

 then solution of copperas and pure sulphuric acid added to it, 

 it evinced no reaction of nitric acid, but this must necessarily 

 have been the case if the crystalline mass consisted of nitrous 

 acid, sulphuric acid and water. I likewise in this case di- 

 vided the solution into two parts, and added to the one por- 

 tion a trace of nitric acid, boiled this portion even somewhat 

 longer, and yet obtained a distinct reaction of nitric acid in 

 the portion to which nitric acid had been added, while the 

 other portion showed not the least trace. Nor did I omit to 

 add to the diluted boiled solution, after cooling, a solution of 

 hypermanganate of potash, and by that means firmly con- 

 vinced myself that no nitric acid had been formed by diluting 

 with water, and that these crystals therefore did not consist of 

 nitrous acid and sulphuric acid, but of a combination of sul- 

 phuric acid, nitric oxide and water. 



But if, after the operation is terminated and the vessel re- 

 mains filled with nitric oxide, atmospheric air be so long blown 

 into the vessel that it again becomes colourless, then indeed a 

 slight reaction of nitric acid is obtained after boiling, which 

 however certainly arises from the water in the vessel dissolving 

 the nitrous acid formed. The solution was tested as above. 



These, then, are the crystals which are formed in the lead 

 chambers in the preparation of English sulphuric acid, and 

 always will be formed when an excess of nitric oxide in com- 

 parison to atmospheric air and sulphurous acid is present, a 

 portion of the nitric oxide then changing only into nitrous acid, 

 which oxidizes the sulphurous to sulphuric acid, and this then 

 immediately enters into combination with the nitrous oxide ; 

 nay, they will be formed even with an excess of nitrous acid 

 and atmospheric air, the sulphuric acid formed decomposing 

 the nitrous acid into nitric acid and nitric oxide, with which 

 it combines. It is therefore requisite, in order to avoid the pro- 

 duction of these crystals in the preparation of sulphuric acid. 



