216 Analysis of ike magnetidal Pyrites. 



the cubic and dodccaedral pyrites found near Soria, from 

 which he obtained about 20 per cent, of siilphur ; and^ 

 having observed that the residuum possessed the properties 

 of the sulphuret which lias been commonly prepared in la- 

 boratories, he concluded that the sulphur obtained from the 

 pyrites is the excess of that proportion which is requisite to 

 form the sulphuret, the proportions of which, therefore, he 

 by synthesis ascertained to be, as I have above stated, = 

 37*30 of sulphur, and 62-50 of iron, or (jO of sulphur com- 

 bined with 100 of iron; and lastly, having formed 318 

 grains of tliis sulphuret froui 200 grains of iron filings, he 

 distilled the sulphuret with an additional quantity of sul- 

 phur in an inferior degree of heat, a,nd obtained 378 gra,ins 

 of a substance which, excepting density, was similar to th? 

 common martial pyrites *. 



It is hovvevei^ to be regretted, that Mr. Proust did not 

 make a regular analysis of the pyrites of Soria, and of the 

 residuum after distillation; for (unless these pyrites are very 

 diflerent from those which I have examined) he would most 

 probably have found the proportion of sulphur greater thari 

 that which he has assigned to natural pyrites in general. 

 This, at least, there is great reason to suppoge, if we allow 

 that most or all of the pyrites have been formed in the humid 

 way, by which, we may conceive, a larger proportion of 

 sulphur may be introduced into the compound than can 

 take place in high degrees of teniperature. And this opi- 

 nion is corroborated by the results of my analyses; for, in- 

 stead of finding the general proportions to be 47*36 of sul- 

 phur and 52-64 of iron, the mean result of these analyses 

 is very nearly the reverse, being 53-24 of sulphur and 46*70 

 of iron. 



Mr. Proust is also of opinion, that the pyrites which 

 contain the smallest quantity of sulphur are those which 

 ar(^most liable to vitriolization ; and, on the contrary, that 

 those which contain the largest proportion, are the least 

 affected by the air or weather f. This opinion of the learned 

 professor by no means accords with such observations as I 

 have been able to make; for the gubic, dodecaedral, and 

 other regularly crystallized pyrites are liable to oxidizement, 

 so as to become what are called hepatic iron ores, but not 

 to vitriolization ; whilst the radiated pyrites (at least those 

 of this country) are by nnich the most subject to the latter 

 cficct ; and therefore, as the results of the preceding ana,- 



* Jouftwl (if Vbr/siqu^, tonic liv. p. 92, 

 f liiiU. tome liii. ji. 91. 



lyses 



