THE VARIATION OF ANGLES OBSERVED IN CRYSTALS. 
499 
Several determiDations were made of the same solution at different temperfrtures, 
and indicated that the index is diminished liy about '0001 for each degree of rise in 
temperature between the above temperatures. The fifth column gives the indices 
reduced to 19°. 
The whole series can only be regarded as a somewhat crude first attempt to trace 
the changes of refractive index with the composition in strong solutions, and only 
with a view to the subsequent measurements made with a growing crystal. Samples 
of several of the liquids were measured at the same time by the hollow jDrism method 
in order to check the results. 
1’33825 by minimum deviation. 
1’33623 by minimum deviation. 
No. 20 gave, at 17°, the values 
1’33855 by total reflection, 
No. 30 gave, at 17°, 
1’33638 by total reflection. 
No. 32 gave, at 17", 
1’33497 by total reflection, 1’33424 by minimum deviation. 
The above results, plotted on a curve with m for abscissa and /x for ordinate (as in 
Diagram I), give points which lie nearly upon a straight line, and indicate both that 
I 333 
1-335 
1-340 
I 
: 1-345 
I 
1-350 
1-355 
1-360 
X 
X 
X X 
Saturated at 19"C 
Diagram 1.—Alum. 
