TPTE VARIATION OF ANGLES OBSERVED IN CRYSTALS. 
513 
(1) A saturated solution of potasli-aluiu contains aljout 8’5 grammes of the 
substance in 100 grammes of solution ; 
(2) The liquid in contact witli a growing crystal contains about 9’3 grammes 
of the substance in 100 grammes of the solution. 
Specific Gravity of Solution in Contact with a Growing Crystal of Potash-alum. 
The refractive index of the liquid in contact with a growing crystal having been 
determined, it seemed desirable to determine also its specific gravity. 
A solution was therefore made containing 9’3 grammes of K-alum per 100 grammes 
of solution, and the following observations were made :— 
Temperature. Specific gravity. 
14°.1‘0458 referred to water at 14° C. 
This agrees very closely with the value obtained by constructing a curve from the 
values found by Gerlach and quoted by Landolt and Bornstein, ‘ Physikalisch- 
Chemische Tabellen,’ 1894, p. 203. 
The refractive index of this solution was determined by the method of total 
reflection with a glass prism of G0° 10|-', and refractive index 1’62151, immersed in the 
liquid. The value olAained was :— 
At 14°. 1-34310. 
The index, as determined from the curve of Diagram I., would be 1-34336 at 14° C. 
(2.) Sodium Chlorate. 
Sodium chlorate has a refractive index of 1-5151 for sodium light, according to 
Kohlrausch, and we have already found that the index of a saturated solution of 
the substance at 16° is about 1-38754 ; with these values, and using cube faces for the 
surfaces of the reflection and emergence, i.e., using a prism of angle 90°, the angle of 
total reflection should be 23° 40f', and the angle of emergence 26° 0|-'. 
A fairly good cube of sodium chlorate growing in its solution yielded readings for 
total reflection from each of the four cube faces in one zone; the best of these 
corresponded to the angle of emergence 9 — — 26° 5'. 
Assuming the angle a to be 90°, and taking the value 1-5151 for the index of the 
crystal, we get p = 1-3870 for the index of the liquid in contact with the crystal. 
A second crystal gave 9 = — 25° 56', a = 89° 59', and, therefore, p = 1-38801. 
A third crystal gave the following very good readings at 15°, the observations 
being made late at night when the crystal was growing steadily and uniformly. 
VOL. CCII.-A. 3 U 
