6 
DR. A. E. H. TUTTON ON THE 
Of the 36 angles compared, 33 show differences on replacing potassium by ammonium 
in the same direction as when rubidium or caesium are introduced instead of potassium, 
the only three exceptions being when the differences are very minute. In 32 of the 
33 cases the changes are greater than when rubidium is introduced, and in 11 cases 
they exceed the effect produced by introducing caesium for potassium. 
Cleavage .—There is a good cleavage parallel to r'{20l}, as usual in this series. 
Also a good cleavage was found parallel to b {010}. 
Volume. 
Relative Density. —Five determinations of specific gravity by the immersion 
method, 
using methylene iodide and 
benzene 
as the immersion 
liquid, gave 
following results :— 
I. 
Density for 18°‘9/4° 
1 '9240 
For 20°/4° 
. P9238 
II. 
„ 19°'4/4° . . . 
1‘9238 
„ 20°/4° . 
. 1/9237 
III. 
„ 18°*8/4° . . . 
P9228 
„ 20°/4° . 
. P9226 
IV. 
„ 18°'2/4° . . . 
1'9222 
„ 20°/4° . 
. P9219 
y. 
„ 19°l/4° . . . 
P9219 
„ 2074° . 
. 1*9217 
Mean . 
. 1*9227 
The value accepted for 20 /4° is therefore T923. 
Perrot* obtained the value 1’92 (three individual values 1‘920, 1'920, and P927). 
Molecular Volume. — ^ ° = 203'91. Perrot gives 205. 
d P923 b 
Molecular Distance Ratios {top>ic axial ratios ).—- 
x : w = 61426 : 8*3312 : 41656. 
Redeterminations of Densities of Potassium , Rubidium , and Ccesium Nickel 
Sulphates. —-These were carried out in order to render all results involving the 
molecular volumes of the four salts strictly comparable, the same immersion liquid 
being used under like conditions. 
In earlier density determinations made with these salts the pyknometer method was 
employed. 
I. 
Potassium Nickel Sulphate , K 2 Ni (S0 4 ) 2 .6H 2 0. 
Density for 19°'0/4° . . . 2*2363 For 20°/V . . 
. 2*2361 
II. 
17°'7/4° 
. . . 2*2378 
„ 2074 o . . 
. 2*2373 
III. 
„ 18°T/4° 
. . . 2*2357 
„ 20°/4° . . 
. 2*2353 
IV. 
„ 19°*6/4° 
. . . 2*2374 
„ 2074 o . . 
. 2*2373 
The value accepted for 20°/4° 
is 2*237. 
Mean . 
. 2*2365 
* ‘Arch, des Sciences phys. et nat., Geneve,’ 1891, 23. ‘Dissertation, Geneve,’ 1890, 47. 
