ARTIFICIAL FELDSPARS. 



35 



and to make a careful study of their heating and cooling curves under 

 atmospheric pressure the conditions under which anorthite and the 

 plagioclases crystallize, the relations between the amorphous and crys- 

 talline forms, the sintering of crystalline and vitreous powders, in 

 short, their entire thermal behavior, as we had done with the borax. 

 At the same time it was our purpose to make careful determina- 

 tions 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 relations 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 very exceptional value. 

 His analyses (see Part II) of the slides form an important part of this 

 discussion. We are also indebted to Mr. W. Lindgren of the United 

 States Geological Survey for valuable assistance in the microscopical 

 study of our products. 



Analyses of Artificial Feldspars. 



The constituents used in our syntheses were precipitated calcium 

 carbonate, anhydrous sodium carbonate, powdered quartz (selected 

 crystals), and alumina prepared by the decomposition of ammonium 

 alum. None 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 were carefully calcined and cooled in a 

 desiccator before weighing. To obtain a homogeneous product, the 

 weighed constituents were mixed as thoroughly as possible mechani- 

 cally and heated in large covered platinum crucibles (ioocc. capacity) 

 in a Fletcher gas furnace.* 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, 



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

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



