On the Cimbiftations of Metals vjith Sulphur. i\^ 



So that Inftead of metallic fulphurets, oxided metallic fulphurets and metallic hydro- 

 fulphurets, we ought to fay fulphurated metals,^ fulphurated' metallic oxides, and fulphuro- 

 hydrogenated metallic oxides. 



But cuftom has predominated in chemiftry, cither becaufe the preference has been dic- 

 tated by the facility of pronunciation, or becaufe the terms themfelves are lefs harfli. This 

 however is of no great importance, as it is fufficient that the elements of bodies fliould be 

 expreffed by their names, and the value of thefe names fhould be precifely underftood. 



Concerning the aftion of the acids on the metallic fulphurets. 



Sulphuric acid. 



Whenever the fum of the affinities of oxigen for a metallic fubftance, and of the me- 

 tallic oxide formed by the fulphuric acid, exceed thofe of the metal for fulphur, and of 

 oxigen for the fulphureous acid, there is conftantly a decompofition of the metallic- fulphu- 

 rets i and the refult is a metallic fulphur and fulphurous acid. All thefe conditions are not 

 conftantly neceflary, but every one of them concurs in accomplifhing the new combinations 

 which are formed, and accelerating the procefs. There are neverthelefs cafes, in which 

 for want of one of thefe conditions no aftion takes place between the bodies. 



The fulphuric acid for example, decompofcs the natutal fulphurated oxide of iron, or 

 martial pyrites very well, but the muriatic acid cannot decompofe it, becaufe the fulphur 

 in this cafe is not attracted by any body, whereas in the other cafe it is attracted by the 

 fulphuric acid, which it converts Into fulphuric acid ; for though I am alTured by many 

 fafts, that the iron in martial pyrites Is oxided nearly to the point at which it Is cafily fo- 

 luble in acids, neverthelefs thefe compounds cannot be decompofcd without the formation 

 of a great quantity of fulphurous acid. 



This opinion is confirmed by the conditions required for the fuccefs of the operation. 

 In faft, the complete decompofition of pyrites is not effefted but by means of heat, and a 

 large quantity of concentrated fulphuric acid ; for it Is evident, that in this cafe the acid Is 

 required not only to faturate the oxide of iron, but alfo the fulphur. I might alfa urge in 

 proof of the fame opinion, the greater affinity of the muriatic acid for the oxide of iron 

 which It cannot neverthelefs feparate from the fulphur in thofe circumftances. It may 

 feem aftonlfhing, that the nitric acid, which has a lefs affinity with Iron, fliould neverthe- 

 lefs decompofe the martial pyrites with fo much eafe ; but we muft not deceive ourfelves 

 in this refpeft, by fuppofing that the acid takes the oxide of iron from the fulphur by a 

 ftronger affinity, for It is on the contrary, by giving a new quantity of oxigen to that fub- 

 ftance, that its affinity for the fulphur is remarkably dimlnlfhed. The fulphur does not 

 unite in fa£t with iron oxided to the maximum, and if by any peculiar procefles thefe 

 fubftances become combined, a portion of oxigen is then feparated. 

 ' Though the muriatic acid cannot decompofe the fulphurated oxide of iron, it decom- 

 pofcs on the contrary with the greateft facility the fulphuret of Iron, in which the metal 

 is not oxigenated. But in this cafe three forces a£t at once, namely, that of the iron on 



O-a ' the 



