DECOMPOSITION OP SULPHATES BY HEAT. SI 



phurets and sulphates; 2d, that to effect this separation does 

 not require so high a temperature as is necessary to decom- 

 pose the sulphates." 



*' Lastly iu distilling a metallic oxide and its sulphuret, a Metallic oxide 

 great deal of siil| hurous acid is obtained, and a little sul- distilled with 

 phate: but, if the temperature be sutficiently high, nothing 

 remains but sulphuret, or merely oxide, according to the 

 proportions employed." 



** Now we are acquainted with the various circumstances. Theory of the 

 that may present themselves in the roasting of" a sulphuret, roasting of sul- 

 it is easy to give the theory of it. To roast a sulphuret is, as 

 the ultimate result, to separate the sulphur by the the simul- 

 taneous action of air and heat. The products obtained 

 vary in general according to the temperature, and to the 

 sulphuret roasted. At an ordinary red heat these sulphu- 

 rets, the metal of which combines but difficultly with sul- 

 phuric acid, yield scarce any thing except sulphurous acid. 

 Those, on the contrary, that condense it strongly, yield also, 

 it is true, sulphurous acid ; but at the same time sulphuric 

 acid is produced, which remains combined with the oxides. 

 At a very high temperature, superior to what would be ne- 

 cessary to decompose the sulphates, all sulphurets yield 

 only sulphurous acid. When once sulphate is formed, it 

 may be decomposed by a more powerful action of heat; or 

 still better by those parts of the sulphuret, that have not yet 

 undergone any change. In fine, when other portions have 

 lost their sulphur, and are oxided, they are capable of 

 taking the sulphur from those that still retain it, and con- 

 verting it i'lto sulphurous acid.** 



The author has availed himself of the facility, with which, Examination 



in the decomposition of sulphates, the sulphuric acid °f .^^^S"™?"* 



^ , , .11 sitionofsuU 



yields Us two component parts, sulphurous acid and oxigen, phuric and 



to ascertain the composition of this acid. He has found, sulphurous 



that 100 parts by measure of sulphurous acid gas take 47*79 



of oxigen gas to form sulphuric- acid ; and, admitting the 



proportions given by Klaproth for the sulphate of barytas, 



he thence deduces the composition of sulphurous acid, which 



is 100 sulphur to 91*68 of oxigen, 



Mr. Gay-Lussac afterward describes the ingenious ex peri- Sulphuric 



ment, in which he decomposed pure sulphuric acid simply *"^ de«onr- 



E 2 by 



