80 On the Desulphwatlon oj Metals. 



This experiment demonstrates in an indisputable man- 

 ner the decomposition of the sulphate of lead by the sul- 

 phuret, or rather that of the sulphuric acid which it contains, 

 by the sulphur and the lead of the galena. The sulphurous 

 acid certainly proceeds both from the oxygenation of the sul- 

 phur, and from the demi-decomposition of the acid, as I am 

 convinced that no sulphate remained in the residue, I re- 

 peated this decomposition, employing equal parts of galena 

 and of sulphate ; the sulphurous acid disengaged was more 

 abundant, and there remained in the retort a mixture of 

 oxide and of sulphuret; from which I concluded, that if, in 

 the first experiment, the proportion of sulphuret of lead 

 was too weak, it was too strong in the latter. I also made 

 another attempt to attain some proportions rigorously suf- 

 ficient for the mutual decomposition, and endeavoured at the 

 same time to assure myself of the oxidation of the lead con- 

 tained in the galena in a metallic state. I put fourteen gram- 

 mes of sulphate, well mixed with eight grammes of sul- 

 phuret, in a crucible, which I allowed to become red-hot 

 in a gradual manner. I remarked that a "considerable 

 crackling was produced, occasioned by the disengagement 

 of the sulphurous acid. I did not take the crucible from the 

 fire until I saw its contents melted. I found two substances 

 well separated ; the one occupying the bottom of the crucible 

 was mtreiv melted sulphuret of lead, without any mixture 

 of ductile lead; the other presented all the characters of the 

 oxide of lead called gla^ss of lead; this part was a combina- 

 tion of oxide and of silesc\ proceeding from the materials of 

 lite crucible, without unv marks of sulphate of lead. 



This experiment proved that the lead of the galena wa9 

 oxidated at the expense of the sulphuric acid ; but it did 

 not show the quantity of galena necessary to the complete 

 decomposition of the sulphate. 1 am of opinion, how- 

 ever, that the proportion of one-part of the former to two 

 of the latter is sufficient ; besides, it closely resembles the 

 proportion which calculation gives us of the composition of 

 these substances. 



The following are the natural consequences of these facts: 

 1st. The galenja and the sulphate of lead are mutually de- 

 composed 



