On Metallic Sidphurets. 209 



'do not, however, afford one example of variable sulphura- 

 tions. Iron, hitherto, is the only metal which appears 

 capable of being sulphurated in two proportions, and these, 

 instead of having any thing variable, are on the contrary 

 constant and fixed, as are those of its oxidation. 



" I am in opposition to Proust, who pretends that sul- 

 phur has been fixed for iron, by the invariable law of pro- 

 portions\, at 60 per cent." 



This result, however, is as certain as invariable, what- 

 ever be the number of times the trial is made : he himself 

 gave this opinion, to which Berthollet refuses his assent. 



He says, " Pyrites may contain a variable surplus, as far 

 as twenty parts and more, &c." 



I cannot discover a similar variation*. Iron is either at 

 60, or at 90, or 100. The first sulphuret is that which we 

 usually make in our laboratories, for the decomposition of 

 water; and the second is pyrites itself. In a word, the 

 case with sulphuration of this metal is the same as with 

 oxidation. The principle which presides at one of these 

 combinations, presides certainly at the other; and if neither 

 nature nor art exhibit to us any where intermediate states 

 between these terms, we ought not to be forward to admit 

 variable sulphurations. 



" If heat can more easily expel this sulphur, considered 

 as foreign, this is a common property, &c." 



Sulphur separated from iron by the action of fire cannot 

 be qualified with ihe name of foreign, because it is a neces- 

 sary element of a combination, which a high temperature 

 destroys, to reduce it to another which can support it. 

 The sulphur which we extract by distillation, from an argil, 

 a sulphate, a stony concretion. Sec. is foreign to their es- 

 sence, but the same cannot be said of a pyrites. If I 

 made use of these expressions, it was contrary to my in- 

 tention. 



" This chemist admits that black copper is sulphuret 

 dissolved by copper. This solution exhibits in reality suc' 

 cessive proportions of sulph\ir and copper, &c." 



This manner of speaking, employed by Berthollet, ought 

 to excite surprise : it tends to throw obscurity on distlnc-' 

 tions which are however clear. Wlien sulphur is prepared 

 in a copper crucible, a sulphuret of 28 per cent, is obtained, 

 and copper holding in solution variable quantities of that 

 sulphuret : the latter may be separated from the copper 



* "Jn.rnalde Physique, p. 90. vol. liv. 



Vol. 21. No. 83. .-/pnV ISO,"). O without 



