142 j^Ttntij^is of the magJiel'icat Pijrltss^ 



learnea professor of chemistry at Madrid, published iwci 

 memoir?, in which he states that there are two sulphure*> 

 .of iron, the one being artificial and the other natural. Tiie 

 first is the sulphuret which is formed in laboratories, bv 

 adding salphur to red-hot iron, or by exposing both of them 

 to heat in a retort. This is distinguished from the second 

 sulphuret (which is the common martial pyrites) by its easy 

 solubility In acids, especially in muriatic acid, by the form- 

 ation of sulphuretted hydrogen gais during the solution of 

 the sulphuret in the last-named acid, by its colour, and by 

 its inferior density. 



According to Mr. Proust, the first or artificial sulphuret 

 is composed of 6o parts of sulphur, combined with lOO 

 parts of iron ; whilst the second sulphuret, or common py- 

 rites, consists of 90 parts of sulphur and 100 Of iron. 



He moreover observes, that the sulphur of the first sul- 

 phuret is ditlicultlv separated ; but that the excess which is 

 in the second sulphuret, or common pyrites, is easily ex- 

 pelled, and is that portion which is obtained by distillation, 

 the residuum being then reduced to the state of the first sul- 

 phuret*. 100 parts, therefore, of this substance, are com- 

 posed of 62-50 of iron and 31-50 of sulphur ; and lOO parts 

 of con)iTion pvritcs are, according to this statement, com- 

 posed of 52'(54 of iron and 47'3G of sulphur. 



These proportions Mr. Proust considers as the minimum 

 and maxinnmi of the sulphureSs of iron. For the latter he 

 allows some variation ; but the composition of the former 

 he resrards as fixed by the invariable law of proportions t j 

 althoiioh he observes, that it has not as yet been discovered 

 in the mineral kingdom +. 



In support of these assertions Mr. Proust states, 



1 . That the pvrites found near Soria, when distilled in 

 a retort heated to redness, afforded nearly 20 per cent, of 

 sulphur. 



2. That the residuum of the above distillation had lost 

 the exttTual characters and chemical properties of pyrites, 

 and had assumed those of the artificial sulphuret of iron. 



• Jomtuil dg Phvslque, tome liii. p. S9, and tome liv. p. 89. From 

 p-^. 91 and 91 of one liv. it is evident thsr the author docs not mean to 

 assert that the first sulphuret contains do per cent, of sufphur j but that 

 100 parts of iron arc combined with 60 of sulphur, and form 160 of the 

 sulphuret. In' like manner, when 90 of sulphur are united with roo 

 of iron, a subvsnce analogous to common pyrites is formed, which weij^hs 

 190 grams or p .rts, 



+ "jovr^'il de Physique, tome liii. p. 90. 



'■ " L?. rcijiic inindral, jusqu'ici, ne nous a point encore prcsente le 

 fcr sulfurc au minimum.'" — Journal de Pbyi^que, tome liv. p. 93. 



3. That 



