•308 On ih( Combinatiotti of the Metals with Sulphur, 



So that inftead of metallic fulphurets, oxided metallic fulphurets, and metallic hidroi* 

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

 hidrogenated metallic oxides. 



But ufage has prevailed in chemiftry, whether from facility of pronunciation, or the 

 greater fmoothnefs of the terms. However this is of no great importance, and if the 

 elements of bodies be clearly underftood from the terms, it will be fufEcient. 



Concerning tlie aElion of the acids upon the metallic fulphurets. 

 - Sulphuric acid. 



"Whenever the fum of the affinities of oxigen for the metallic fubftancc, and of the oxide 

 thus formed for the fulphuric acid, is greater than that of the metal for fulphur and of 

 oxigen for the fuiphureous acid, there will conftantly be a decompofitian of the metallic 

 ■fulphuret, and the refult will be a metallic fulphate and fuiphureous acid. The whole of 

 thefe conditions are not always neceflary : but each concurs in the accomplifhment of the 

 new combinations which are formed, and accelerates the operation. There are neverthe- 

 ]efs cafes, in which for want of one of thefe conditions the bodies do not a£i at all upon 

 leach other. 



The fulphuric acid for example, decompofes the natural fulphurated oxide of iron or 

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

 in this cafe is not attra£led by any body, whereas in the former it is attradled by the ful- 

 phuric acid, which it converts into fuiphureous acidj for though I have found by many 

 fafts, that the iron in martial pyrites is oxided nearly to the point in which it is eafily 

 foluble in acids, it cannot however be decompofed without forming a gc^at quantity of 

 / fulphuric acid. 



This opinion is confirmed by the conditions neceflary for completing the operation. In 

 fa£^, the complete decompofition of pyrites cannot be effefled without heat, and a great 

 quantity of concentrated fulphuric acid. For it is evident here, that acid is not only re- 

 ijaired-for the faturation of the oxide of iron, butalfo for that of the fulphur. I could 

 likewife urge in fupport of the fame opinion, the greater affinity of the muriatic acid for 

 •the oxide of iron, which neverthelefs it is incapable of feparailng from the fulphur undeir 

 thefe circumftances. It may feem ftrange that the nitric acid, of which the affinity to iroJi 

 js lefs flrong, fliould neverthelefs decompofe the martial pyrites with fo much facility 3 but 

 we ought not to deceive ourfelves by fuppofing, that it is by a ftronger affinity that this 

 iacid takes the oxide of iron from fulphur ; for it is on the contrary, by affording a new 

 quantity of oxigen to the iron that the affinity of the metal for the fulphur becomes Angu- 

 larly diminiftied. In reality, fulphur does not Unite with iron oxided to the maximum, and 

 when by certain peculiar procefl'cs thefe two fubftances are combined, the effect alwayis 

 iiappens from a feparation of part of the oxigen. 



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

 pofes on the contrary the fulphuret of iron, in which the metal is not exigenated, with the 

 greateft facility. But in this cafe three fonces a€t at once—- namely, that of the iron on 

 4 the 



