PURE SULPHURIC ACID. 95 



acid, is oxidized into sulphuric acid, while nitric oxide is 

 evolved ; and he proposed to burn sulphur alone without nitre, 

 and pass the gas through the first crude acid containing nitric 

 acid. Turner's patent is based on this fact (Rep. Pat.'Inv. 

 1845). The lead chamber is made very low (3 ft. high), and 

 its horizontal surface increased. The bottom is covered with 

 crude acid of 1.5-1.6, containing 3-4 per cent, strong nitric 

 acid. The sulphurous acid is drawn into the chamber by 

 pumps, and in order to avoid loss, this acid and the nitric 

 oxide are passed through three lead vessels, the two first con- 

 taining the mixture of nitric and sulphuric acids, and the last 

 sulphuric acid of 1.7. This process is said to yield 50 per 

 cent, more oil of vitriol than the former method. (?) 



Schneider (Comptes Rendus, xxv. 931) has succeeded in 

 converting sulphurous into sulphuric acid, by means of pumice- 

 stone peculiarly prepared, without the necessity of leaden 

 chambers or iron retorts. We do not know how the pumice 

 is prepared. A process was patented, many years since, for 

 making oil of vitriol from sulphurous acid, by means of pla- 

 tinum-sponge, but was not successfully carried out as a manu- 

 facturing process. 



Paul Gilbert Pretier has patented a process (Ch. Gaz. vi. 

 88) for making fuming sulphuric acid by distilling the bisul- 

 phates, as follows : Alkaline sulphates are placed in a stone 

 retort, and acidulated by the addition of oil of vitriol. Heat 

 being gradually applied, the distillate collected in receivers 

 is clear and colorless. 



Pure Sulphuric Acid. — A. A. Hayes (Silliman's Journ. 

 1848) takes the acid of 1.76 at that stage of the process for 

 manufacturing the commercial article, when it is ready for 

 transferring from the leaden evaporators to the concentrating 

 vessels of platinum. This weak acid, while hot, is treated 

 with nitrate of potassa, which renders it colorless by destroy- 

 ing the coloring matter. It also removes much of the hydro- 

 chloric acid, and converts the arsenious and sulphurous into 

 arsenic and sulphuric acids. The remaining hyponitric acid 

 jft expelled by the addition of 3 Jo of sulphate of ammonia. 



