324 SULPHUR. 



water upon this crystalline solid is remarkable, occasioning its 

 decomposition with effervescence ; a hydrate of sulphuric acid 

 remains behind, and the nitrous acid is expelled in a state of 

 decomposition, as nitric oxide and peroxide of nitrogen. The 

 result then of these changes has been the formation of a certain 

 quantity of sulphuric acid ; and the nitric oxide is again restored 

 to the gaseous atmosphere ; where if it meets a second time 

 with oxygen, sulphurous acid and moisture, it may give occasion 

 to a repetition of the same changes, and the formation of an 

 additional proportion of sulphuric acid, and do so again and 

 again, so long as it continues to meet with both oxygen, sul- 

 phurous acid, and moisture. The nitric oxide is thus a medium, 

 of transference, by which the oxygen of the air reaches the 

 sulphurous acid, and a small portion of the former may be the 

 means of converting a large quantity of the latter into sulphuric 

 acid. 



In the manufacture upon the large scale, the sulphurous acid 

 is converted into sulphuric acid, in oblong chambers of sheet- 

 lead, supported by an external framework of wood. Sul- 

 phurous acid from burning sulphur, nitric acid vapour and 

 steam are simultaneously admitted into the leaden chamber ; 

 and the sulphuric acid formed accumulates in the liquid state 

 upon the floor of the chamber. The diagram below represents 

 one of the most improved forms of the chamber, with its appen- 

 dages. 



FIG. 37. 



a represents the water boiler, with its furnace for supplying 

 the chamber with steam ; b, the section of a small chamber in 

 brickwork, or furnace, called the burner, upon the floor of 

 which the sulphur burns, and in which there is a tripod sup- 

 porting an iron capsule, which contains the materials for nitric 

 acid, namely oil of vitriol and either nitre or nitrate of soda. 

 The heat of the burning sulphur evolves the nitric acid from 

 these materials, and consequently the sulphurous acid becomes 

 mixed with nitric acid vapour, which it carries forward with it, 

 by a tube represented in the figure, into the chamber, where 



