28 
DR. A. E. H. TUTTON ON THE 
Molecular Distance Ratios {topic axial ratios ).— 
X ' f • 0J ~ 6'2670 : 8'4690 : 4‘1761. 
Redeterminations of Densities of Rubidium and Caesium Manganese Sulphates. 
Rubidium Manganes 
e Sulphate, 
RffMn (S0 4 ) 2 . 6H 2 0. 
I. 
Density for 14 '9/4° 
. 2'4617 
For 20°/4° . . . 
2'4605 
IT. 
o 
<-0 
o 
. 2'4613 
„ 20°/4° . . . 
2'4604 
III. 
,, 16°'l/4° . . 
. 2'4607 
o 
—b 
0 
O 
CM 
2'4597 
IV. 
„ 16°'6/4° . . 
. 2'4622 
o 
o 
CM 
2'4614 
Mean . 
2'4605 
?cepted value for 20 /4°, 2'461. 
Former pyknometer value 2'459. 
C Vesium Manganese 
Sulphate, 1 
OsoMn (S0 4 ) 2 . 6H 2 0. 
I. 
Density for 18 '9/4 
. 27397 
For 20°/4° . . . 
27394 
II. 
19°'3/4° . . 
. 27420 
o 
-b 
o 
o 
(M 
27418 
Ill. 
,, 19°'7/4° . . 
. 27409 
„ 2074 " . . . 
27408 
IV. 
„ L7 q '2/4° . . 
. 27373 
ID 
0 
*- 
0 
27365 
Mean . . . 2'7396 
Accepted value for 20°/4°, 2740. Former pyknometer value 2'738. 
The next table affords a comparison of the volume constants of the three salts, 
employing the new densities. 
Volume Constants of the Manganese Group. 
Salt. 
Molecular 
weight. 
Specific 
gravity. 
Molecular 
volume. 
Topic axial ratios. 
RbMn 
sulphate . 
522-36 
2-461 
212-26 
X ; 
6-2404 : 
8•4536 
CO 
4-1846 
NH4M11 
388-42 
1-831 
212-13 
6-2670 : 
8-4690 
4-1761 
CsMn 
O • 
616-36 
2-740 
224-95 
6-3286 : 
8-7004 
4-2745 
From this table it will be apparent that the molecular volume and topic axial ratios 
of ammonium manganese sulphate are very close to the values of these constants for 
the rubidium salt. The molecular volume and the ratio a> are very .slightly lower, and 
the ratios x and f slightly higher. 
Optics. 
Orientation of the Optical Ellipsoid. —-The symmetry plane h {010} is the plane of 
the optic axes, and the sign of double refraction is positive. The first median line is 
the axis y of the optical indicatrix, and the second median line corresponds to the 
a refractive index. 
