Brown.] -^4 J [-^yiay 18, 



expression of the condition of the iron in the molecule and as embodying 

 in a quantitative way the result of my investigations into its constitution. 

 It will be noticed that the sulphur of the Fe"S2 is made to link entirely 

 with iron, 



S 



Fe^ 



S 

 I 



S— Fe< 



Structural formula of pyrite. Fe", I 



^S— Fe< 



S 



I 



S 

 Fe^: 



If ferric iron be considered as Fe''' — Fei- It is only necessary to connect 

 the ferric Fe atoms with bonds, but it seems to me that ferric iron is more 

 likely Fe'", and at any rate this is the simplest way to regard it. A very 

 striking proof of the correctness of the idea expressed in this structural 

 formula that Fe'^Sj in pyrite has its sulphur all linked to iron is alforded 

 in the experiments on oxidation of the mineral by means of the electric 

 current as detailed above. It will be recalled that the amount thus 

 oxidized was between 21 and 22 per cent. Now if two molecules of FeSa 

 be split off from the above formula, say those linked by sulphur to sulphur 

 there would remain a saturated compound much more difficult to decom- 

 pose (theoretically) than the pyrite molecule illustrated and the amount 

 of sulphur thus removed would be by calculation 31.33 per cent. This 

 action could be thus illustrated : 



S 



// 



Fe 



tt S 



S— Fe< , , Fe< I 



/ g decomposed g/ ^i 



Fcv I by the current Fe< | 



S_Fe<'* ^o"^d give ^ ^^Fe< I 



S tt 



i 



s 



♦ 



Of course this structural formula is only intended to represent the 



