504 FRANK D. ADAMS 



similar distortion of the fluorite was produced while the green color 

 of the original mineral became much paler. The change in color of 

 the fluorite which, as noted above, was produced in every instance 

 by the pressure is a very curious phenomenon. In three of the 

 experiments the change consisted in the substitution of a much paler 

 tint of green for the deeper green color which the mineral possessed 

 originally. In the other two cases, where the deformation had been 

 if anything more intense, the original green color actually changed to 

 pale purple or violet, a color which is often possessed by the fluorite 

 from Derbyshire and elsewhere. The reason ior this change is un- 

 known and will probably remain so until the nature of the fugitive 

 colors displayed by this mineral have been discovered. It was at first 

 thought that the change in question might have been brought about 

 by the heat of the molten alum in which the mineral was embedded 

 and that it might thus have been induced before the pressure had been 

 applied. Crystals of the fluorite from both localities were accordingly 

 taken and embedded in molten alum in the usual way, but it was found 

 on removing the alum by solution that no change in color whatsoever 

 had resulted from this treatment. The change in color therefore must 

 be due solely to the action of pressure. 



Apatite. — A small crystal of opaque greenish apatite from one of 

 the Canadian localities, probably in Ottawa County, Quebec, measur- 

 ing a little less than 1.25 inches (31.75 mm.) in height, and about 

 o . 5 inch (12.7 mm.) in diameter, was selected. The crystal showed the 

 usual prismatic and pyramidal faces seen in the specimens from this 

 district, as well as small basal planes. It was placed, resting on one 

 of the pyramidal faces, in a copper tube of the same dimensions as 

 that employed in the last experiment, but 1.25 inches (31.75 mm.) 

 high. The tube was then filled up with molten alum in the usual 

 way and brass plates were placed at either end. The whole was then 

 slowly squeezed down until the tube showed signs of rupture, the 

 time occupied by the deformation being 55 minutes and the maximum 

 load being 43,000 pounds (19,405 kilos). 



On dissolving away the alum the apatite crystal was found to have 

 been crushed to a coarse powder at either end. The central part — rep- 

 resenting about one-half of the original crystal — however, remained as 

 a solid mass, and showed portions of the six prismatic faces. Crossing 



