SPECIFIC GRAVITY. 



57 



Determination of Moisture in i gram of Powdered Mineral 

 upon Exposure to the Air. 



<^ = finer than. > = coarser than. 



In the last two groups, note that the moisture in graded portions of 

 the same sample varies with the fineness. 



We also verified the conclusion of Bunsen* that this adsorbed mois- 

 ture is not removed at temperatures only slightly above ioo, but 

 requires 6oo to 8oo 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 magnitude as those usually 

 obtained for the water content in feldspar analyses,! where again, of 

 course, the finer the sample is ground for the analysis the greater the 

 possible error from this cause. It may be 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 determinations 

 could be made was limited only by the possibility of obtaining com- 

 plete crystallization within a reasonable time. Thus Ab 2 An! was 

 reheated many times before a constant value was reached. Ab 3 Ani 

 required 17 days and Ab 4 An! was not completely crystallized in any of 

 our attempts. Crystalline albite was produced under other condi- 

 tions. 



* Wied. Ann., 24, p. 327, 1885. 



| Dana, System of Mineralogy, 6th ed., pp. 314 et seq. 



