40 W. E. Ford — Chemical, Optical and other Physical 



the series was found to be 0-045 or, if the plus and minus signs 

 were taken into consideration, it was only + 0-002. From this 

 it would seem as if the values assigned above to the specific 

 gravities of the various pure garnets were at least very nearly 

 correct. 



Figures 1 to 8 show the facts outlined above in graphical form 

 by means of equilateral triangular plotting. The black dots 

 represent the positions on the charts of the different analyses 

 containing two or three constituents. The heavy broken lines 

 indicate the probable limits of the possible mixtures of each 

 series. The heavy solid lines give the loci of points represent- 

 ing the different mixtures possible with a certain index of 

 refraction. The lighter solid lines show in a like manner the 

 mixtures possible with a given specific gravity. Therefore, if 

 the refractive index and specific gravity of a garnet are known, 

 together with its chief components as determined by qualitative 

 tests, it ought to be possible in the majority of cases to predict 

 rather closely what its chemical composition should be. 



A further study was made of the analyses quoted on page 34 

 and 35 to discover, if possible, any interrelationships between the 

 indices of refraction, specific gravities and molecular weights. 

 The garnets, the specific gravities of which were unknown, were 

 naturally omitted from consideration. Analysis 20 was also 

 eliminated because of the small amount of data available con- 

 cerning the uvarovite molecule. The results of this study are 

 given in the table below and are also shown in a graphical form 

 in figs. 9 to 12. 









n. — 1 





F 





n 



Analysis 



91. 



Sp.Gr. 



~cT 



Mol. Wt. - 



~oT 



G 



Pyrope 



1-705 



3-510 



2008 



404-5 



240 



5 



914 



Grossularite 



1-735 



3 530 



2082 



451-7 



227 



6 



196 



1 



.... 1-736 



3-506 



2099 



453-0 



228 



6 



249 



3 



.... 1-742 



3-715 



1997 



436-6 



213 



5 



959 



4. 



.... 1-742 



3-525 



2104 



454-0 



224 



6 



280 



6..- 



... 1-760 



3-837 



1980 



445-3 



200 



5 



970 



7 



1-763 



3-633 



4-040 



2100 

 1925 



463-6 

 498-0 



210 

 184 



6 

 5 



316 



8 



.... 1-778 



826 



9 



.... 1-781 



4-025 



2100 



487-3 



184 



5 



878 



10. 



.... 1-792 



4-230 



1925 



495-9 



170 



5 



698 



11 



.... 1-800 



4-058 



1940 



493-8 



176 



6 



019 



Spessartite 



1-800 



4-180 



1904 



496-4 



171 



5 



843 



12 



.... 1-801 



4-255 



1882 



496-8 



168 



5 



750 



13 



.... 1-801 



4-093 



1957 



479-4 



188 



5 



977 



14 



1-806 



4-169 



1933 



496-2 



170 



5 



917 



15 



.... 1-807 



4-163 



1938 



484-9 



170 



5 



935 



16 



.... 1-808 



3 960 



2040 



474-0 



179 



6 



250 



17 



1-810 



4-273 



1895 



495-8 



165 



5 



812 



18 



1-813 



4-135 



1966 



486-4 



169 



6 



035 



Almandite 



.... 1-830 



4-250 



1952 



499-1 



161 



6 



039 



21.... 



1-864 



3 803 



2271 



495-7 



170 



7 



132 



22 



.... 1-888 



3-660 



2425 



505-7 



170 



7 



701 



23.... 



.... 1-888 



3-801 



2336 



505-4 



163 



7 



415 



Andradite 



.... 1-895 



3-750 



2386 



509-3 



164 



i 



600 



