Properties of the Feldspars. 



127 



Determination of Moisture in 1 Gr. of Powdered Mineral upon 

 Exposure to the Air. 



Mineral. 

 Orthoclase (natural glass) 

 Ab 1 An 5 (artificial glass ) 



" ( 

 At^An, ( 



Ab 

 Ab 



(natural 



( " 



cryst. ) 



glass ) 

 cryst. ) 



" ) 



" ) 



Orthoclase (natural cryst.) 

 " (same sample ) 



Orthoclase (artificial glass) 

 " (portion of same) 



< = finer than 



Fineness (mesh). 

 <150 



selected, coarse 

 <100 >120 

 <100 >120 

 <100 >120 

 coarse 

 <150 



<I20 >150 

 <150 

 still finer 



Moisture. 

 •0061 gr. 

 •0000 

 •0010 

 •0007 

 •0010 

 •0006 

 •0069 



•0011 gr. 

 •0031 



•0059 



everything <^100 -0065 gr. 



>150 -0022 



> — coarser than 



In the last two groups, note that the moisture in selected 

 portions of the same sample varies with the fineness. 



We also verified the conclusion of Bunsen* that this adsorbed 

 moisture is not removed at temperatures only slightly above 

 100° but requires 600° to 800° — equivalent to a low red heat. 

 Several samples for which the moisture had been determined 

 were laid away in corked test tubes for a number of weeks, 

 after which redetermination gave exactly the former value. 



It is worth noting in this connection that these measured 

 quantities of adsorbed water are of the same order of magni- 

 tude as those usually obtained for the water content in feldspar 

 analyses,f where again, of course, the finer the sample is 

 ground for the analysis, the greater the possible error from 

 this cause. It may he that a part and occasionally all of the 

 moisture usually found in these analyses is adsorbed and the 

 significance of its presence there mistaken. 



The number of feldspars of which specific gravity deter- 

 minations could be made was limited only by the possibility of 

 obtaining complete crystallization within a reasonable time. 

 Thus Ab 2 An 1 was reheated many times before a constant value 

 was reached. Ab 3 Anj required 17 days and Ab 4 An a was not 

 completely crystallized in any of our attempts. Crystalline 

 albite was produced under other conditions. 



The specific gravities of the glasses and of so many of the 

 crystalline mixtures as we could obtain are tabulated below : 



*Wied. Ann., xxiv, p. 327, 1885. 



f Dana, System of Mineralogy, 6th ed. 



p. 314 et seq. 



