British Mineralogy. 177 



hind. This was not found to be the case ; the mineral, although 

 not crystallized, appeared to the eye (and when magnified also) 

 to be perfectly homogeneous, and did not in any way convey the 

 impression to the examiner of being a mixture. Moreover 

 several other specimens, not only from this mine but from an- 

 other mine at Craigmuir, about to be referred to, and also from 

 a mine in Norway, possessed all so close a similarity in their per- 

 centage composition that the results appear rather to indicate 

 that this mineral may be a definite compound. 



The analyses of a large number of specimens of nickeliferous 

 pyrrhotine from various localities appear to show the probability 

 of another definite compound containing about 4 per cent, of 

 nickel. This is extremely common, and has been met with by 

 the author in Norway, Sweden, Italy, Germany, and the United 

 States. A combination of 15 (Fe 7 S 8 ) + NiS would by calculation 

 yield — 



Sulphur .... 38-78 



Iron 57-12 



Nickel .... 4-10 



10000 



In Greg and Lettsom's c Mineralogy of Great Britain/ an ana- 

 lysis of the ore from this mine is cited (p. 297), and stated to 

 be an average of the rough ore. The numbers given are — 



Iron 4376 



Nickel .... 14-22 



Sulphur .... 34-46 



Silica 5-90 



Lime 1*45 



99-79 



No other analysis of any British specimen of this mineral ap- 

 pears recorded. Numerous determinations of the percentage of 

 nickel in the ore from this mine, made by the author, never afforded 

 results anything like approaching to the above ; even with the 

 most careful picking, and employing only the purest and richest 

 parts in the analysis, the highest percentage of nickel found did 

 not in any case materially exceed 11 per cent. The specimens 

 analyzed were obtained from His Grace the Duke of Argyll (the 

 proprietor of the mine) in 1851 ; and subsequently others were 

 taken by the author out of the lode, on the occasion of two visits 

 to the mine in 1853 and 1855 ; the precise specimen the ana- 

 lysis and description of which is here brought forward was ob- 

 tained in 1855. An average quantity of the ore sampled in 

 1851 afforded— 



Phil. Mag. S. 4. Vol. 35. No. 236. March 1868. N 



