MORSE. — STUDIES ON FLUORITE. 607 



Experimental Arrangements. 



The present series of experiments consisted only in heating fluorite 

 in a vacuum and making a complete analysis of the gases evolved at 

 various temperatures, varied from about 250° to 700°. Samples of 

 gas were pumped out at various stages of the heating and the gases 

 corresponding to the reaction (whatever it may be) at various tempera- 

 tures for the same specimen of fluorite were separately analyzed. For 

 the lower temperatures the mineral was heated in a glass or porcelain 

 retort or a glass or porcelain tube in an air bath. For the higher 

 temperatures the fluorite was heated in a porcelain tube in a combustion 

 furnace, and the temperatures are therefore only rough approximations. 

 The retort or tube was connected with a cooled receiver in which the 

 liquid distillate condensed, and beyond the receiver with a Toepler 

 vacuum pump of the form usual for the collection of gases. The 

 gases were collected over mercury at the delivery end of the pump, and 

 passed into the usual apparatus for gas aualysis wholly through sealed 

 glass connections. For the determination of the rare gases a second 

 Toepler pump was connected with the first through a series of combus- 

 tion furnaces containing reagents necessary for the removal of nitrogen. 

 The purified residue was finally passed through the second pump into 

 a Geissler tube for spectroscopic examination. In order to obtain a 

 sufficient quantity of gas for an accurate test for helium, argon, etc., 

 a large quantity of fluorite (10 kilos) was heated in an iron retort and 

 the total residue of the whole volume of gas obtained (about 7 liters) 

 was sent through for the final spectroscopic examination. 



The usual weight of fluorite taken for an analysis was 250 gms. and 

 the amount of gas obtained from this amount of the mineral varied 

 greatly. Some of the colored and not very transparent Weardale 

 fluorites yielded as high as 500 c.c. of gas for this amount of material, 

 while other clearer specimens from the same locality gave as low as 

 50 c.c. Some American fluorites having a deep green color gave only 

 about 20 c.c. of gas, even when they were heated to 700°. 



The vacuum reached before heating began was usually about 1 mm. 

 At ordinary temperatures no diminution in the vacuum, such as would 

 be caused by the escape of gas from cavities, was observable after 

 24 hours. 



Analyses of the Gases from Fluorites. 



The following are characteristic sets of analyses from a few of the 

 twenty samples analyzed. The results obtained on different samples of 



