1 1 6 On the Coinlhtations of Metals lutth Sulphur, 



the oxigen of the water, that of the fulphur on the hidrogcn of the fame fubftance, and 

 that of the metallic oxide formed by the mdriatic acid. Under thefc circumftances fulphu- 

 rated hidrogenous gas is conftantly difengaged. 



The fulphuric acid which does not decompofe the fulphurated oxide of iron, unlefs it be 

 concentrated and boiled, decompofes the fulphuret of iron in the cold, and the more eafily 

 when diluted with a certain quantity of water. The reafon of this is evident, and need, 

 not be explained. 



Though a great quantity of water is inimical to the adlion of the acids upon metallic 

 fulphurets in general, it is however lefs fo with regard to iron than other metals, becaufe 

 fulphurated hidrogen does not decompofe the folutions of Iron in acids. 



Concerning the Sulphuret of Lead. 



In the natural fulphuret of lead or galxna the lead exlfts in the metallic (late, for which, 

 reafon when this mineral fubftance is put in contadl with muriatic acid, fulphurated hidro- 

 gen is formed even in the cold. It appears even when fulphur is united to the oxide of lead- 

 That metal lofes its oxigen to unite to the fulphur for the combination by this means ob* 

 tained, is perfeftly fimilar to natural galena. It is eafy to conceive how the reduction of 

 the lead is obtained in this procefs : a portion of the fulphur combines with the oxigen, 

 and forms fulphuric acid, which is driven off by the heat, while another portion of the 

 fulphur unites to the metallic lead. The redu£lion of the lead, and the formation of galena, 

 take place nearly in the fame manner, when a folution of this metal in an acid is mixed 

 with a folution of fulphurated hidrogen, or any hydro-fulphuret whatever. There is how* 

 ever this difference, that in the laft cafe it is hidrogen, which takes oxigen from the lead,, 

 and forms water at the fame time that the fulphur and the metal, which meet in a very 

 extreme ftate of divifion, combine without heat in the midft of the fluid. There is alfo 

 another difference, that the galena formed by this procefs contains a little more fulphur. 

 than the natural compound, as is proved by the fmall quantity of fulphur which is fepar 

 rated from that fubftance by a very gentle heat, and then leaves a compound in a ftate. 

 abfolutely fimilar to that of common galena. 



From thefe fa£ls it refults that the muriatic acid, and probably all the acids which adi. 

 upon the oxide of lead by their mafs and their concentration, do lofe their lead by the 

 a£l:ion of the fulphurated hydrogen, as foon as thefe two forces, or even one of them is 

 weakened j but whatever may be the quantity of acid united to lead, or any other metal,, 

 the decompofition of the fait will take place, if any hydro-fulphuret he employed in fufil- 

 cient quantity. 



We cannot be furprized at the diminution of the affinities of the acids for the metallla 

 oxides by water, nor their more powerful aftion on thefe fubftances by their maffes.. 

 Antimony, mercury, bifmuth, and lead itfelf, afford ftriking examples of this. 



We know in fa£t, that by mixing a great quantity of water with their concentrated folu^- 

 tions, very confiderable precipitates are formed, which have been erroneoufly taken for 



pur« 



