38 



ISOMORPHISM AND THERMAL PROPERTIES OF FELDSPARS. 



ABjANj. 

 FIRST PREPARATION. 



Melting temperature, 1500 . 



In one instance, while cooling the molten mass at a rapid rate, we 



obtained a result which has a most important 



bearing on the relation of the feldspars to one 



another, which will be referred to again in the 



concluding discussion of the experimental data. 



When the charge had cooled, it was found to 



consist of a compact mass of rather large crystals, 



radial in structure, at the bottom of the crucible 



(fig. 8), and a beautiful, transparent glass above. 



It was easy to separate the crystalline portion 



from the glass and to analyze the two separately. 



The composition of the two portions is practically 



identical, save for a slightly higher percentage of 



-iron in the crystals. (A small quantity of iron 



was contained in the quariz used in preparing 



the feldspars.) In harmony with this latter 



circumstance the color of the crystals was a 



decided amethyst brown, while the glass was but slightly tinted. 



The analyses follow: 



Ab!An 5 . 



Fig. 8. 



