THE VARIATION OF ANGLES OBSERVED IN CRYSTALS. 
507 
(4.) Re f}'active Indices of Solutions of Sodium Nitrate. 
The refractive index of a saturated solution of sodium nitrate was found as 
follows : — 
fl. 
t. 
1-38880 
19f 
By minimum deviation. 
1-38837 
22 
1-38770 
24-5 
51 55 55 
1-38873 
17-5 
,, total reflection. 
Supersaturated and sti'ong solutions were next examined by the total reflection 
method (prism of 44° 52', index I •51704). In Series L, 20 cub. centims. of a saturated 
solution were placed in the trough and examined with the same totally reflecting 
prism as before, and were diluted by successive additions of 2 ctAd. centims. of water 
ujj to No. 15. Nos. 16 and 17 were taken after addition of 6 cub. centims. and 
4 cub. centims. of water respectively. In this series Nos. 1 and 2 were taken on one 
day and the remainder on the following day. The results are given in Table XII. and 
are represented by crosses in Diagram IV. 
1-400 
Diagram IV.—Sodium Nitrate. 
3 T 2 
