^74> MAGNETICAL PYRITES. 



in muriatic acid, by the formation of fulphuretled hidrogeri 

 gas during the folution of the fulphuret in the lalt named acid, 

 by its colour, and by its inferior denfity. 

 Artificial ful- According to Mr. Prouft, the firft or artificial fulphuret is 

 phuret, 6 ful- compofed of 60 parts of fulphur, combined with 100 parts of 

 iron; natural, iron; whilii the fecond fulphuret, or common pyrites, confifts 

 9 fulphur and io f 90 p arts f f u ip nur and 100 of iron. 



The excefs of He moreover obferves, that the fulphur of the firft fulphuret 



fulphur is eafily \ s difficultly feparated ; but that the excefs which is in the fe- 



pyritcs 6, burnot cont * ^ u 'p^ uret » or common pyrites, is eafily expelled, and is 



the other por- that portion which is obtained by diftillation, the refiduum 



tlon ' being then reduced to the ftate of the firft fulphuret *. J 00 



parts, therefore, of this fubfiance, are compofed of 62.50 of 



iron and 37.50 of fulphur; and 100 parts of common pyrites 



are, according to (his ftatement, compofed of 52.64 of iron 



and 47.36 of fulphur. 



They are the Thefe proportions Mr. Prouft confiders as the minimum 



maxima and ^ max ; mum f t } ie {' u | p hurets of iron. For the latter he 



minima or the « 



fulphurets. allows fome variation ; but the compofition of the former he 



regards as fixed by the invariable law of proportions f; al- 

 though he obferves, that it has not as yet been dlfcovcred in ilie 

 mineral kingdom J. 



In fupport of thefe affertions, Mr. Prouft ftates, 

 Experiments of 1 . That the pyrites found near Soria, when diftilled in a 

 Prouft on this retor t healed to rednefs, afforded nearly 20 per cent, of ful- 

 phur. 



2. That the refiduum of the above diftillation had loft the 

 external characters and chemical properties of pyrites, and 

 had affuined thoie of the artificial fulphuret of iron. 



* Journal de Phyfique, Tome LIII. p. %9, and Tome LIV. p. 89. 

 From pp. 91 and 92 of Tome LIV. it is evident, that the author 

 does not mean to afferr, that the firft fulphuret contains 60 per cent. 

 of fulphur; but that 100 parts of iron are combined with 60 of 

 fulphur, and form 160 of the fulphuret. In like manner, when 

 90 of fulphur are united with 100 of iron, a fubfiance analogous 

 to common pyrites is formed, which weighs 190 grains or parts. 



See alfo our Journal, I. 109, 269, 253, for tranflations of thefe 

 excellent memoirs. 



f Journal de Phyfique, Tome LIII. p. 90. 



\ " La regne mineral, jufqu'ici, ne nous a point encore pre- 

 fente le fer fulphure au minimum." Journal de Phyfique, Tome 

 LIV. p. 93. 



5 3. That 



