266 ANALYSES OF SOME CANADIAN MINERALS. 



2. Silver Glance : from Thunder Bay, Lake Superior. 



The sample consisted of a small mass of distorted crystals (combina- 

 tions of cube and octahedron), perfectly sectile and malleable. Sp. gr. 

 = 7-31. Decomposition was effected by nitric acid; the silver weighed 

 as Ag CI ; and the sulphur partly as S, and partly as Ba SO*. The ' 

 analysis of 1-933 gramme yielded in per centage values : 



Sulphur 13-37 



Silver 86-44 



Copper faint trace 



3. Magnetic Pyrites : from Madoc (lot 18, con. 2). 



Some carefully selected fragments, apparently quite free from FeS?, 

 were taken for the analysis, and decomposed by chlorhydric acid with 

 subsequent addition of nitric acid. They were strongly magnetic, and 

 the mass from which they were separated exhibited well marked mag- 

 netic polarity. Their sp. gr. was equal to 4-485 ; but most examples 

 from this locality, in consequence of intermixed silica or siliceous rock- 

 . matter, vary, as regards sp. gr., from about 4-2 to 4-3. 



The picked fragments yielded : 



Sulphur 39-98 



Iron 51!-66 



The sample contained no trace of either nickel or cobalt. An assay 

 of 50 grammes, for gold, left nothing on the cupel. 



In another examination, the sulphur was determined by decomposing 

 a portion of the finely powdered mineral with nitre and carb. soda in a 

 porcelain crucible. 1-155 gramme gave 3 377 grammes of Ba SO4. 

 This is equivalent to 40-17 per cent, of sulphur. 



4. Arsenical Pyrites : from Tudor, in Hastings county. 



This sample, if I may so call it, was not analysed, as it consisted 

 merely of a few minute but well-defined crystals, given to me some 

 time ago by my colleague, Professor Croft. Two of these little crys- 

 tals, examined by the blowpipe, shewed unmistakably the re-action of 

 cobalt ; and the presence of this metal appears to be connected with a 

 crystallographic peculiarity in these and other crystals of mispickel. 

 The more common crystals of this mineral, consist, it is well known, 

 of a rhombic prism combined with the planes of a side-polar or brachy- 

 dome i ^ . In these Tudor crystals, the brachydome in question is 

 replaced by two of less obtuse type, namely, J ^ and ^ . Now, the 



