ABSTRACTS 



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PHYSICAL CHEMISTRY.— n,e binary system: NasAlsSisOg {nephel- 

 ite, carnegieite) — CaAl2Si208 (anorthite). N. L. Bowen. American 

 Journal of Science, 33 : 551-573. 1912. 



The study of the system Na2Al2Si208 — CaAl2Si208 was undertaken 

 because of the importance of these compounds as rock-forming con- 

 stituents. It was found that the soda compound exhibits enantiotropism 

 with the inversion point at 1248°. The low temperature form (nephel- 

 ite) crystallizes in the hexagonal system with a habit similar to that of 

 natural nephelite. The high-temperature form is triclinic. It has no 

 natural analogue and has been given the name carnegieite. Carnegieite 

 melts at 1526°. 



The lime compound occurs only in the triclinic form, anorthite, and 

 melts at 1550°. 



Both carnegieite and nephelite are capable of holding the lime com- 

 pound in solid solution, the former 5 per cent and the latter as much as 

 35 per cent. 



The effect of solid solution on the inversion-point was well shown by 

 the system. The temperature of inversion rises considerably as the 

 amount of the lime compound in solid solution increases. 



The optical constants of the components were carefully determined. 

 Crystals of the artificial nephelite were measured on the goniometer 

 and their hexagonal nature confirmed. It was especially gratifying to 

 be able to determine definitely the variation, with composition, of the 

 optical properties of the hexagonal mix-crystals (nephelite). With 

 increasing proportion of the lime molecule the birefringence of 0.004 

 (negative) becomes less, passes through zero, and finally becomes 0.002 

 (positive) . 



The problem as a whole, although in some measure complicated, was 



found capable of very definite laboratory solution. The extension of the 



study to include the potassium-bearing nephelites has already been 



be^un. N. L. B. 



90 



