44 Bowles — P yromorpliite from British Columbia, Can. 



variety differs from the green only in its smaller content of 

 arsenic. He records an analysis which indicates that the green 

 pyromorphite contains 0*66 per cent arsenic pentoxide, while 

 the yellow variety contains none. The analyses given above 

 show a somewhat similar relationship ; for, although arsenic is 

 present in both, there is a larger per cent in the green 

 variety. This fact, and the presence of a larger quantity of 

 iron oxide in the yellow variety, are the only marked differ- 

 ences brought out by the chemical analyses. 



Specific Gravity. — This was determined by means of 

 a Muthmann capillary-tube pycnometer. Extremely pure 

 material of both varieties was obtained, and a comparatively 

 large amount (about eight grams) was used, in order to insure 

 accurate results. Crystal fragments about the size of fine shot 

 were emj)loyed. Several determinations were made, and the 

 results are tabulated below : 





Yellow Variety 



Green Variety 



I 



'z-oii 



7-055 



II 



7-016 



7-052 



III 



._ 7*012 



7-046 



IV. _. 



7*014 



7-053 



Average 



7-013 



7*051 



From the above results it is evident that the green pyro- 

 morphite has a higher density than the yellow\ Dana* gives 

 the specific gravity of the pure mineral a rather wide range, 

 varying from 6*5 to 7'1. This British Columbian pyro- 

 morphite then approaches the higher limit set by Dana. 

 The results obtained are slightly higher than those of Bauer, f 

 who gives a variation of 6*9 to 7*0. 



In conclusion I desire to acknowledge valuable assistance 

 rendered by Prof. T. L. Walker of the University of Toronto, 

 under whose direction the investigations were conducted. I 

 am indebted to Prof. W. A. Parks of the same institution for 

 selecting the material, and for information regarding its occur- 

 rence and associations. 



Mineralogical Laboratory, University of Michigan, 

 Ann Arbor, Mich., March 8th, 1909. 



* System of Mineralogy, p. 770. 



f Lehrbuch der Mineralogie, 2te Auflage, 1904, p. 805. 



