DECOMPOSITION OF SULPHATES BY HEAT. S3 



preceding, and which are acid and insoluble, give out sul- 

 phuric acid, oxtgengas, and sulphurous acid. 



2d. In the roasting of metallic sulphurets, the products metallic-8«I- 

 vary according to the temperature, and according to the phurets, 

 sulphuret. At a very high temperature, sulphurous acid is 

 given out in quantities so much the greater in proportion as 

 the oxide is capable of condensing it more strongly ; and 

 when it has but a very weak affinity for it, no sulphurous 

 acid is formed, 



« 3d. AH the earthy sulphates, which are naturally acid, earthy sul- 

 are decomposable by fire, giving out sulphuric acid, oxigen phate», 

 gas, and sulphurous acid. 



" 4th. The neutral alkaline sulphates are not decoraposa- and alkaline 

 ble by fire, that of ammonia excepted : but when they are ^" ^ *^^*' 

 capable of forming crystallizable salts with excess of acid, 

 condensing it, and diminishing its volatility, part of this 

 excess of acid is changed iuto oxigen gas and sulphurous 

 acid. 



** 5th. Sulphates treated in the fire with phosphoric or Actioo of 

 boracicacid yield sulphuric acid, oxigen gas, and sulphurous P^°^P^onc 

 acid, acid. 



" 6th. Sulphuric acid is composed of 100 parts sulphur- composition 

 ous gas, and 47*79 oxigen gas, by measure. of sulphuric 



«« 7th. 100 parts of sulphur by weight require 5061 of J^J ^"Jj^^"^' 

 oxigen, to convert them into sulphurous acid, and 85*70 to 

 form sulphuric acid. 



" 8th. Sulphuric acid is decomposable by heat alone into Sulphuric 

 oxigen gas and sulphurous acid gas. ^'^^'^a^u^^' 



** 9th. A great elevation of temperature is not favourable Manufacture * 

 to the production of sulphuric acid; on the contrary^ it is of sulphuric 

 detrimental to it. The instant of the combustion of sul- **^' ' 

 phur, sulphurous gas only is obtained, whether it take place 

 in the open air or in oxigen gas; and the sulphuric acid 

 obtained in leaden chambers must be the result of the action 

 of nitrous gas and of the air on the sulphurous acid, as well 

 as of the action the last mentioned gas exerts on oxigen 

 by means of water. 



