MONOCLINIC DOUBLE SULPHATES CONTAINING AMMONTIJM. 
33 
Determination of True Optic Axial Angle in Bromonaphthalene. 
Light. 
Li 
C . . 
Na. . 
T1 . . 
Cd . . 
F . 
No. of plate 
perp. 1 M.L. 
Observed 
2IL, 
No. of plate 
perp. 2 M.L. 
Observed 
2 IL> 
1 
o / 
61 34 
la 
o / 
94 26 
2 
61 34 
2 a 
94 29 
3 
61 29 
3 a 
94 24 
1 
61 31 
la 
94 21 
2 
61 32 
2a 
94 25 
3 
61 28 
3a 
94 20 
1 
61 18 
la 
93 52 
2 
61 22 
2 a 
94 0 
3 
61 21 
3 a 
93 53 
1 
61 9 
la 
93 27 
2 
61 13 
2 a 
93 25 
3 
61 8 
3a 
93 26 
1 
61 0 
la 
92 58 
2 
61 5 
2 a 
92 59 
3 
61 3 
3 a 
92 58 
1 
60 50 
la 
92 38 
2 
60 54 
2 a 
92 38 
3 
60 54 
3a 
92 37 
Calculated 
2 Ya. 
Mean 
2Y 
69 47' 
69 45 
69 44, 
69 47' 
69 46 
69 45, 
69 48' 
69 48 
69 51. 
69 53' 
69 57 
69 53. 
69 58' 
70 2 
70 1 
70 O' 
70 3 
70 3 
69 45 
69 46 
69 49 
69 54 
70 0 
70 2 
Murmann and Rotter obtained for 2E 114° 45', and for 2V a 69 u 9' (no wave-length 
specified). 
A determination of 2E at 70° with Plate 2 showed that the optic axial angle in air 
diminishes by about 4 for 55° rise of temperature. 
Dispersion of the Median Lines. —The inclined dispersion is again small in 
ammonium manganese sulphate, the first median line lying nearer by lCf only to the 
axis a for red lithium light than for greenish-blue F light. The determination was 
carried out by immersion of the Plates 1, 2, and 3 in toluene. 
The optic axial angle of ammonium manganese sulphate is shown in the following 
comparative table to be slightly larger than that of the rubidium salt. 
Optic Axial Angles 2Y a of the Manganese Group. 
AmMn sulphate. 
HbMn sulphate. 
| 
CsMn sulphate. 
Li. 
o / 
69 45 
o / 
67 10 
O f 
60 10 
C. 
69 46 
67 8 
60 7 
Na. 
69 49 
67 5 
59 57 
T1 . . . . 
69 54 
67 1 
59 46 
F .... 
70 2 
66 55 
59 28 
VOL. OCXVI.-A. 
F 
