180 Mr. D. Forbes's Researches in 



pyrites and magnetic pyrites taken from mineral lodes and erup- 

 tive rocks, proved that nickel was very rarely found in iron 

 pyrites (Fe S 2 ) when not accompanied by pyrrhotine, but that 

 cobalt was very commonly present in small quantity, — and, on 

 the other hand, that cobalt was equally seldom in magnetic py- 

 rites (Fe 7 S 8 ) if unaccompanied by iron pyrites, — also that when 

 both these metals were present in a specimen of pyrites, the 

 nickel greatly preponderated when the pyrites in question was 

 magnetic (pyrrhotine), whilst the reverse was found to be the 

 case when it was the bisulphide of iron or ordinary so-called iron 

 pyrites. 



Sulphide of Iron and Nickel from the Craigmuir mine on the 

 side of Loch Fyne, about eight miles below Inverary, the lode 

 traversing metamorphic strata, and disturbed by intersecting trap- 

 pean dykes. — The specific gravity of the pure mineral was found to 

 be 4 - 602 at 60° F. The general characters of the mineral corre- 

 sponded very closely with those of the specimen from Inverary, 

 the colour alone differing in having a somewhat more dark-bronze 

 tint, probably due to the entire absence of iron pyrites in the 

 specimen submitted to examination. The blowpipe reactions 

 were quite identical with those of the Inverary mineral, and the 

 chemical analysis was conducted in precisely the same manner. 

 The results of the analysis of a specimen (as pure as possible) 

 taken out of the lode in April 1855 was as follows : — Mineral 

 employed 34*15 grs., which yielded 0*13 gr., or 0'38 per cent, 

 insoluble matter, consisting entirely of quartz with a few flakes 

 of silvery mica ; 0*03 gr. free sulphur ; 94*26 grs. sulphate of 

 barytes; 24*04 grs. sesquioxide of iron, from which 0*02 gr. 

 arsenic acid was subsequently separated by precipitation with 

 sulphuretted hydrogen in the state of sulphide. Another por- 

 tion, 20*03 grs. in weight, was employed for the determination 

 of the nickel and cobalt, and yielded 2*81 grs. of the mixed 

 oxides, in which the cobalt was determined by Plattner's method. 

 These data make the chemical composition, when tabulated, ap- 

 pear as follows : — 



Sulphur . . 

 Iron 



Nickel . . 



Cobalt . . . 



Copper . . 



Arsenic , . 

 Silica and mica 



37*99 



50*87 



10*01 



1*02 



traces 

 004 

 0-38 



100*31 



The results correspond closely with those obtained when the 



