MACNF.T1CAL PYRITES. 275" 



3. That when to this refiduum a quantity of fulphur was 

 added, and the whole was diftiiled in a degree of heat not too 

 great, the 20 per cent, of fulphur, which had been feparated 

 by the firft diftillation, was, by this, again reftored; and the 

 mafs in the retort thus recovered nearly the original colour, 

 luftre, and chemical properties of the pyrites. 



4. That, by adding fulphur to iron filings, or fine iron wire, 

 heated to a low red in a retort, a compound is obtained, in 

 which the proportion of fulphur amounts only to about 20 

 or 30 parts ; but, if this compound is again treated with 

 fulphur in a red heat, a fulphuret is formed, which is readily 

 diffolved in acids, and plentifully affords fulphuretted hydro- 

 gen gas. 



This is (he real minimum of the fulphurets of iron, fixed 

 by the invariable law of proportions, (according to Mr. 

 Prouft,) at 59 or 60 of fulphur and 100 of iron, the former 

 being (as I have already obferved) in the proportion of 37.50 

 per cent. 



5, and Iaftly. That when this fulphuret is again mixed and 

 diftilled with fulphur, (due attention being paid to the degree 

 of heat,) the product is found to have affumed mod of the 

 chemical and external properties of the natural common pyrites, 

 denfity alone being excepted. 



The application of the above obfervations, to the principal The magnetleal 

 fubiect. of the prefent paper, is fufficiently obvious: for, when Py rit f s is that 



. . ■■ ! . ■ -i ■ • r , ^ r which Prouft 



it is contidered, that the magnetical pyrites is lo different from confidered as 

 the common pyrites, in colour, hardnefs, folubility in fulphuric hav '"g keen °nty 

 acid, and more efpecially in muriatic acid, with the copious ' y " * 



production of fulphuretted hydrogen gas; when, by ar.alyfis, 

 it has been found to confift of 36 or 37 of fulphur, combined 

 with about 63 of metallic iron ; and, when the artificial ful- 

 phuret of iron which has been lately defcribed, is proved to 

 agree with the magnetical pyrites in the nature and proportions 

 of its component ingredients, and in every one of the above- 

 mentioned properties ; it is evident that the magnetical pyrites 

 is identically the fame with this fulphuret, which hitherto has 

 remained undifcovered in nature, and has only been known 

 as a product, of our laboratories. In order however more fully 

 to fatisfy myfelf, I made experiments on the artificial fulphuret, 

 which I formed with fulphux and fine iron wire, 



T 2 This 



