52 
DR. A. E. H. TUTTON ON THE 
Observations at higher temperatures were precluded on account of decomposition 
and opacity due to loss of water of crystallisation. 
In the next table the refractive indices of the three cadmium-containing salts are 
compared. 
Comparison of the Refractive Indices. 
Index. 
Light. 
RbCd sulphate. 
NH 4 Cd sulphate. 
CsCd sulphate. 
r 
Li. 
1-4773 
1-4816 
1-4947 
C. 
1-4777 
1-4821 
1-4951 
Na. 
1-4798 
1-4847 
1-4975 
a . . . 
T1. 
1-4823 
1■4875 
1-5000 
F. 
1•4856 
1-4907 
1-5033 
G. 
1-4906 
1-4961 
1-5081 
r 
Li. 
1-4820 
1•4855 
1-4972 
C. 
1-4824 
1-4860 
1-4976 
R J 
Na. 
1-4848 
1-4887 
1-5000 
/*•••• i 
T1. 
1-4872 
1-4915 
1-5026 
F. 
1-4905 
1-4947 
1-5058 
i 
G. 
1-4955 
1-5001 
1-5106 
f 
Li.'. 
1-4919 
1-4927 
1-5034 
C. 
1-4923 
1-4932 
1-5038 
Na . ■ . . . . 
1-4948 
1-4959 
1-5062 
7 • • • • 1 
T1. 
1-4972 
1-4987 
1•5088 
F. 
1-5097 
1-5019 
1-5123 
i 
G. 
1-5061 
1-5073 
1-5172 
Mean refractive 
index ^(ot + fS + y) 
1-4865 
1-4898 
1-5012 
for Na light 
Double refraction, Na v _„ .... 
0-0150 
0-0112 
0-0087 
The refractive indices of the ammonium cadmium salt are just slightly higher than 
those of the rubidium cadmium salt, the relationship being best expressed by the mean 
index given at the foot of the table. The double refraction of the ammonium salt is 
also intermediate between the values for the rubidium and caesium salts, but in this 
case nearer to the caesium salt. 
Axial Ratios of the Optical Ellipsoid .—The values of these ratios are compared in 
the next table. The potassium salt not being available for comparison, only the ratios 
on the basis of the /3 value of each salt = 1 are possible. 
RbCd sulphate 
NH 4 Cd „ • 
CsCd 
Axial Ratios of 
Optical Indicatrix 
a : 0 : y 
0T966 : I : 1‘0067 
0-9973 : 1 : R0048 
0'9983 : 1 : R0041 
Optical Velocity Ellipsoid, 
a : t> : c 
D0034 : 1 : 0‘9933 
R0027 : 1 : 0'9952 
R0017 : 1 : 0'9959 
