218 H. L. Wells — Composition of Pollucite and its 



the comparatively high specific gravity of the American 

 mineral seems to point to still better quality if not to some 

 difference in composition. 



A single piece of the very best quality was selected for the 

 chemical examination, while the water was determined in two 

 other fragments also, because of the evident importance of the 

 water in calculating the formula. Analyses I and II were 

 first made, but, as they did not show a perfect agreement in 

 the determinations of the alkalies, No. Ill was then made with 

 the greatest care. This last is considered the best of the analy- 

 ses and the ratio given is calculated from it, but it will be 

 noticed that the other two analyses confirm this quite well and 

 that they both point to the same formula with almost equal 

 sharpness. 



Water was determined by loss by ignition, as given in detail 

 beyond; the "intense ignitions" were made in small platinum 

 crucibles over a powerful blast-lamp . flame, so that the heat 

 obtained was very high. The material was not dried in any 

 way before weighing. The mineral was decomposed by hydro- 

 chloric acid, and silica, alumina and lime were determined by 

 the usual methods, care being taken to take account of the 

 slight impurities in the silica and alumina. The alumina con- 

 tained a very faint trace of iron, no more than might have 

 been introduced by breaking the mineral up with steel cutters ; 

 no evidence could be found of the presence of other elements 

 in the alumina. The identity of the lime was shown by the 

 spectroscope. 



The alkali-metals were weighed together as chlorides, then 

 caesium and potassium were separated and weighed as platini- 

 chlorides ; the alkali-chlorides in the latter were separated and 

 weighed in order to calculate the proportion of caesia and 

 potash. The potassium spectrum was detected from these last 

 chlorides with considerable difficulty, while they showed no 

 rubidium spectrum whatever. Lithium chloride was separated 

 from sodium chloride, after the removal of the excess of 

 platinum, by the method of Grooch, and the soda was calcula- 

 ted from the difference between the other chlorides and the 

 total mixed chlorides, while in analysis III the sodium chloride 

 was also weighed directly, giving a result which happened to 

 be exactly identical with the indirect determination. This 

 agreement of the direct with the indirect determination of the 

 soda may be considered as an indication that the other alkalies 

 were determined with reasonable accuracy. The lithium was 

 identified with the spectroscope. 



