W. P. Headden — Some Phosphorescent Calcites. 303 



Iceland spar ceased to phosphoresce very quickly ; so did the 

 colorless, the white opaque and the purple pieces of the Joplin 

 mineral, while the yellow was still phosphorescent at the end 

 of an hour. 



Burning magnesium provokes phosphorescence in the yellow 

 but not in the other varieties, Iceland spar included. The 

 duration of this phosphorescence was not determined, but it 

 exceeded ten minutes. 



The time of exposure to the action of these agents varied 

 greatly, but it will be recognized that my object was to study 

 the deportment of these calcites and not the relation of the 

 intensity and duration of the phosphorescence to the intensity 

 and time of action of the agents causing it. The shortest 

 insolation timed was four minutes and it produced a strong 

 phosphorescence. Our insolations were made at various times 

 of the day, from early morning till after 5 o'clock in the even- 

 ing, with apparently equally good results. The yellow calcite 

 emits light when crushed or powdered : the light is yellow and 

 there is no danger of mistaking it for the light emitted when 

 an agate or porcelain mortar is rubbed with its pestle. The 

 yellow calcite becomes phosphorescent when heated. Small 

 pieces heated in an air bath began to phosphoresce when the 

 thermometer indicated a temperature of 60° C, but the larger 

 pieces introduced at the same time did not begin until the 

 thermometer showed 75°. The phosphorescent light emitted 

 by the heated pieces is reddish yellow, almost salmon-colored, 

 and fades rapidly especially if the temperature has been raised 

 to 180° or higher. If the temperature has been raised to 100° 

 and the specimens removed, the phosphorescence fades rapidly 

 at first but afterwards quite slowly. 



Some of the samples burst when heated to 180°, possibly 

 due to liquid inclusions ; the appearance of some of the pieces 

 suggested the presence of such, but none were actually observed. 

 Heating to 200° does not destroy the property of the calcite 

 to become phosphorescent on subsequent insolation, but igni- 

 tion does. 



If a piece of insolated calcite be brought into a heated air 

 bath, the character, intensity and duration of the phosphor- 

 escence is modified and deports itself as though the phosphor- 

 escence had been produced by heating alone. 



The size of the pieces of calcite insolated has but little or no 

 effect on the intensity or duration of the phosphorescence. In 

 one instance a piece weighing less than two-tenths of a gram 

 was the brightest one in the tray and was still recognizable as 

 such at the end of one and a half hours. 



In the large number of insolations made we met with but 

 two exceptions to the statement that the yellow calcites become 

 phosphorescent by insolation. I have not discovered the 

 reason for these two exceptions. The cause was not due to 



