Anali/sh of the inagnnikal Pyr'ites. 141 



^Sulphur 53-<3o 

 No. 4. Radiated pyrites. " " J ^"^^^ 'I'o-AQ 



Specific gravity 46y8. | ■ 



V 100- 



j^Sulphur 54*34 



No. 5. A smallervariety of radiated pyrites.! Iroa 45-68 



Specific gravity 4775. J 



100- 



Considering" the difference in the figure, lustre, and co- 

 lour of these pyrites, I expected to have found a much 

 greater difference in the proportion*; of their component in- 

 gredients j but, as the results are the average of several ex- 

 periments, I have not any reas(m to doubt their accuracy. 



The pyrites crystallized in regular figures, such as cubes 

 and dodccaedrons, according to the above analyses, contain 

 less sulphur and more iron tlian the radiated pyrites, and 

 perhaps than others \vhich are not regularly crystallized. 

 This difference, however, is not considerable ; for the do- 

 decacdral pyrites, which afforded the smallest quantity of 

 sulphur of any of the regularly crystallized pyrites, yielded 

 52*15 ; and the radiated pyrites. No. 5, gave 54* 34 : the 

 difference, iherefore, is only 2-l(>. So that the mean pro- 

 portion of sulphur in all the pv riles which were examined 

 IS 53-2 i per cent.; and, taking the proportion of sulphur 

 in the niagnctlcal pyrites at 36*50 or 37, the diffei-ence 

 between this and the mean of the conuiion pyrites will be 

 10*74 or 16*2-1. The magnctieal pyrites, therefore, is quite 

 ilistinct, as a sulphuret of iron, from the common martial 

 pyrites; and in the following observations I shall prove 

 that a sulphuret consisting of the proportions last men- 

 tioned has till now been unknown as a product of nature. 



§ VI. 

 Although pyrites is one of the most comrnon of mineral 

 substances, yet the discovery of its real nature is compara- 

 tively of a late date ; for it appears that even Agricola 

 (whose knowledge of mineral bodies was certainly great, 

 considering the slate of science in his time) was not ac- 

 uuainted with its characteristic ingredient, namely, iron. 

 According to Henckel, this was first noticed by our coun- 

 tryman Martin Lister, a member of this learned society, 

 who says, " Pi/r'ites pnriis pufiii ferri mctalium est." 



From the time of Menckel, pyrites seems little to have 

 aitracled tlie notice of chemists^ until Mr. Proust, the 



learned 



