and Density of Some Crystallised Silicates. 



265 



synthetic work of the Geophysical Laboratory and the method 

 of preparation and purity are discussed in publications to 

 which explicit reference will be made further on. 



Fig. 1. 



/■sa 



L57 



m 



(•SS 



I.S+ 



1 1-53 



/SZ 



}SI 



X 



o ISO 



1-49 



M f48 



10 



Albite 



10 



J 



so 



60 



eo 



30 100 

 Anorthite 



The indices of refraction of the glasses were determined by 

 the method of minimum deviation and each was checked by two 

 separate wedges. The measurements were made on a Gold- 

 schmidt two-circle goniometer, using lithium, sodium and thal- 

 lium lights, and the angles checked to the nearest minute. 

 The measurements for the two wedges usually checked to 

 within 0-0004 and the probable error is ±0'0003. The results 

 for the measurements of the feldspar glasses are given in 

 Table 1, and are plotted in tig. 1 ; those for the metasilicate3 

 of calcium and magnesium in Table 2 and fig. 2 ; and those of 

 the other silicates of calcium and magnesium in Table 3. 



