106 Day and Allen — Isomorphism and Thermal 



careful determinations of the specific gravities of both the 

 vitreous and the crystalline products, analyses of such portions 

 as might be of special interest, and also to prepare microscopic 

 sections wherever they were likely to throw light on the rela- 

 tions involved. The latter, after preliminary examination, 

 were very thoroughly studied by Prof. J. P. Iddings of the 

 University of Chicago, whose large petrographic experience 

 with mineral crystallites makes his judgment of exceptional 

 value.* 



The constituents used in our syntheses were precipitated 

 calcium carbonate, anhydrous sodium carbonate, powdered 

 quartz (selected crystals) and alumina prepared by the decom- 

 position of ammonium alum. IN one of these contained more 

 than traces of impurities, if we except the quartz, in which 

 0*25 per cent of residue, chiefly oxide of iron, was found after 

 treatment with hydrofluoric and sulphuric acids. All but the 

 calcium carbonate w r ere carefully calcined and cooled in a 

 desiccator before weighing. To obtain a homogeneous pro- 

 duct, the weighed constituents were mixed as thoroughly as 

 possible mechanically, and heated in large covered platinum 

 crucibles (100 cc capacity) in a Fletcher gas furnace.f After 

 some hours heating, during which the temperature usually 

 reached 1500° or more, the product was removed from the 

 furnace, cracked out of the crucibles, powdered, passed through 

 a " 100-mesh " sieve and then melted again. This process 

 probably gives a fairly homogeneous mixture, though a third 

 fusion in the resistance furnace was generally made before 

 determining the constants. 



We prepared in this way albite (Ab), anorthite (An) and 

 the following mixtures of the tw T o : AbjAn^ Ab a An 2 , A^An^ 

 Ab 2 An 1? Ab 3 An 1? A^An^ All of these were obtained in 

 wholly or partially crystalline form, by crystallization from 

 the melt, except albite. The syntheses were controlled by 

 analyses of a number of the products, the results of which are 

 appended. 



Analyses of Artificial Feldspars. 





An 



AbiAns 



AbiAn 2 



Ab 2 Ani 





Found. 



Calcu- 

 lated. 



Found. 



Calcu- 

 lated. 



-u, -, Calcu- 

 Found - lated. 



«• Sid"" 



Si0 2 



43*33 



43-28 



47-10 



47-18 



51-06 51-30 



60-01 59-81 



A1 2 3 



36*21 



36-63 



34-23 



34-00 



31-50 31-21 



24-95 25-47 



Fe 2 Ol 



•29 







•15 







•22 



•29 



CaO 



20-06 



20-09 



17-00 



16-93 



13-65 13-68 



7-09 6-98 



Na 2 



•11 







1-74 



1-87 



3-68 3-79 



7-79 7-73 



100-00 100-22 100-11 100*13 



* See Pt. II of the complete paper, Publications of the Carnegie Institution 

 of Washington. 



f Buffalo Dental Company, No. 41A. A Fletcher furnace of this type, 

 with ordinary city gas pressure and a small blast motor, will melt all of the 

 feldspars. 



