^12 MR. HATCHETT ON MAGNETICAL PYRITES. 



hy nature; and that the compofition of this laft, agrees with 



thofe proportions of the artificial fulphuret which have been 



Hated by Mr. Proiift. 



Ko intermediate But, from this fulphuret or magnetlcal pyrites, I have not, by 



mtnral piodud auaiyfis, as yet been able to difcover any regular or inimediale 



common and the gradations into the common pyrites; for the lead proportion of 



pyrites. fulphur in thefe amounted to 52. 15, and the greateti proportion 

 to 54.34; ib that, between the magnelical and the common 

 pyrites, the difference is confiderable, in the pMroportions of their 

 component fubftances, as well as in their phyfical and chemical 

 properties ; whiltl the difference which I have hitherto been able 

 lo detect in the proportions of fome of the common pyrites 

 (very dilTimilar in figure, luftre, colour, and hardnefs,) has 

 only amounted to 2.19. 

 Ilemarlcs on Mr. Prouft, in a genera! way, confiders common pyrites to 



Prouft's expeii. f^iffer from the firfi fulphuret, or that compofed of 60 parts pf 

 fulphur and 100 of iron, {=37.50 per cent.) by containing a 

 farther" addition of half the above quantity of fulphur, or 90 

 parts of fulphur and 100 of iron, ( = 47.36 per cent.) but this 

 opinion he appears to have formed, in confequence of refults 

 obtained by fynthetical experiments made in the dry way. — . 

 Now, when we conlider how difficult it is to regulate the high 

 degrees of temperature, and what a numerous chain of altera- 

 tions in the relative order of affinities moft commonly refult 

 from alterations in thefe degrees of heat, it feems to me that 

 we cannot rely, with abfolute certainty, on fynthetical experi- 

 ments made in the above way, unlefs they are corre6led, and 

 contratied with analytical experiments made on the fame fub- 

 ftances. But it does not appear, from the two memoirs pub- 

 lifbed by Mr. Prouft, to which I have fo frequently alluded, 

 that that gentleman did more, in refpecl to analyfis, than diftil 

 the cubic and dodecaedral pyrites found near Soria, from which 

 he obtained about 20 percent, of fulphur; and, having ob- 

 ferved that the refiduum po{fe0ed the properties of the fulphu- 

 ret which has been commonly prepared in laboratories, he con- 

 cluded that the fulphur obtained from the pyrites, is theexcefs 

 of that proportion which is requifite to form the fulphuret, the 

 proportions of which, therefore, he by fynthefis afcertained to 

 be, as I have above dated, = 37.50 of fulphur, and 62.50 of 

 iron, or 50 of fulphur combined with 100 of iron; and laftly, 

 having formed 3 1 8 grains of this fulphuret from 200 grains of 



iron 



