604 PROCEEDINGS OF THE AMERICAN ACADEMY. 



luminescences, is the very strong odor which is produced when the 

 mineral is heated or ground to powder in a mortar. Schafhautl 31 

 showed that chlorine monoxide is produced when the famous fluorite 

 from Wolsendorf is heated. Schoubein, Meissner, Schrbtter, 32 and 

 others were of the opinion that the odor produced on heating is due to 

 ozone. Becquerel and Moissan 33 found traces of free fluorine in the 

 gases distilled from some fluorites, and ascribe the odor to this substance. 

 The great majority of all the analyses of the mineral show the presence 

 of small but appreciable quantities of chlorine. 



The odor of all the samples of fluorite which I have examined by 

 heating is what would be called distinctly "empyreumatic " — closely 

 resembling the odor arising from the distillation of wood, and certainly 

 of organic origin. None of the many samples which have been at my 

 disposal have shown any very marked odor on attrition, but a few give 

 an " earthy " odor, not very characteristic, but suggestive of organic 

 origin. 



Inorganic Impurities. 



The most general of these appear to be chlorine, iron, and phosphoric 

 acid, neither of which is a perfectly general impurity, and neither of 

 which is usually supposed to exercise any influence on luminescences. 

 Not long ago Humphreys 34 showed that yttrium is an almost universal 

 impurity in fluorite, using the delicate spectroscopic test for the presence 

 of this strange element. For the present, attention has been confined 

 to those substances which can be volatilized or decomposed by a low red 

 heat, and yttrium compounds would not be included, though the presence 

 of this substance is certainly suggestive. 



Gaseous and Liquid Inclusions in Minerals. 



These have been the subject of much investigation since the discovery 

 of carbon dioxide in liquid form in crystal cavities by Brewster. 35 

 While carrying out this investigation he found that air and water are 

 present in certain fluorites, and since that time carbon dioxide, hydro- 

 gen, nitrogen, carbon monoxide, oxygen, and hydrocarbons have all been 

 reported as existing in the form of inclusions in this mineral. Tilden 36 

 and Gautier 3 ? examined the gases produced by heating many rocks and 



si Liebig's Ann., 46, 344 (1843). 32 Pogg. Ann., Ill, 561 (1860). 



33 C. r., Ill, 669 (1890). 3i Pliys. Rev., 19, 300 (1004). 



35 Edin. Trans., 10, 1 (1826). 36 Roy. Soc. Proa, 60, 453 (1896). 

 37 Bull. Soc. Chim.. 25, 402 (1001). 



