and Density of Some Crystallized Silicates. 



267 



— == — .100, gives the percentage which the index of refraction 



for any intermediate member exceeds the value computed on 

 the assumption that it is an additive function of the end 

 members. In the (Ca,Mg)Si0 3 series this excess is positive 

 and is well beyond the limits of error. The plot of figure 2 

 shows a curve which is sensibly straight throughout its central 

 part but which bends down rather sharply at both ends. The 

 data for the feldspar glass show a negative deviation as indi- 

 cated by the curves plotted in figure 1. These are also sensibly 

 straight throughout their central portion, but bend up at both 

 ends.* 



The specific gravities of the glasses were determined on 

 powder of 100 mesh size in a pycnometer, with water or zylene 

 at 25° C.f Separate determinations on material from the same 

 melt usually checked to 0*002, but the difference is somewhat 

 greater when the powders are from different melts. The values 

 for the specific gravities are given in Tables 1, 2 and 3 in 

 the columns headed D and are plotted in figs. 3 and 4. The 

 values for the feldspar glasses were taken from the data of 



Day and Allen 4 In the column headed — — — .100 is given 



the percentage of deviation of the specific volume from the 



Table I. 





CD <jj 



(1) 



o Per cent 



o Anorthite 



o 



N Li 

 1-4864 



N Na 



N Th 



3 



H 



c 

 c 



1 



; 



3 

 £ 



D 



> 

 II 



c 



G 

 > 

 > 



3 



Ab 



100-00 



1-4891 



1-4916 



■0052 



o-oo 



2-382 



•4198 



o-oo 









1-4865 



1-4889 



1-4917 



•0052 











Ab 2 Aiii__ 



65-37 



34-63 



1-5136 

 1-5134 



1-5168 

 1-5164 



1-5194 

 1-.5191 



•0058 

 •0057 



-0-16 



2-483 



•4027 



+ 0-02 



AbiAii!.- 



48-55 



51-45 



1-5281 

 1-5276 



1-5309 

 1-5306 



1-5335- 

 1-5334 



•0054 



•0058 



-0-18 



2-533 



•3948 



+ 0-11 



AbiAn 2 _. 



32-05 



67-95 



1-5420 + 

 1-5420 



1-5451- 

 1-5453 



1-5480 



1-5482- 



•0060 

 •0062 



-0-16 



2-591 



•3859 



-0-07 



AbiAn 5 . 



15-87 



84-13 



1 -5562 

 1-5565 



1-5600 

 1-5600 



1-5628 

 1-5629- 



•0066 

 •0064 



-0-12 



2-648 



•3776 



-0-15 



An 



o-oo 



100-00 



1-5720 

 1-5718 



1-5756 

 1-5754 



1-5786 

 1-5786 



•0066 

 •0068 



o-oo 



2-700 



•3704 



o-oo 



* For data on similar deviations for isomorphous artificial crystals, see 

 Fock, Zeitscbr. f. Kryst., iv, 583, 1880. 



f Isomorphism and thermal properties of the feldspars, Pub. No. 31, Car- 

 negie Institution of Washington, p. 55. 



X Loc. cit. 



