MONOCLINIC DOUBLE SULPHATES CONTAINING AMMONIUM 
87 
Comparison of the Interfacial Angles (continued). 
Angle. 
KCu sulphate. 
RbCu sulphate. 
CsCu sulphate. 
AmCu sulphate. 
fbo =(010) 
(111) 
o / 
69 50 
o / 
70 8 
70 34 
o t 
70 16 
\os =(1H) 
:(101) 
20 10 
19 52 
19 26 
19 44 
j bo' = (010) 
(111) 
65 3 
65 8 
65 22 
64 57 
1 o's' = (Ill) 
(101) 
24 57 
24 52 
24 38 
25 3 
fsq = (101) 
(011) 
38 32 
37 59 
37 21 
37 59 
< qp = (oil) 
(110) 
85 32 
86 22 
87 27 
87 2 
ips = (HO) 
(101) 
55 56 
55 39 
55 12 
54 59 
fsq = (101) 
(Oil) 
45 17 
45 1 
44 44 
45 33 
Up =(0H) 
(110) 
63 51 
63 22 
63 0 
62 44 
lps' =(H0) 
(101) 
70 52 
71 37 
72 16 
71 43 
r to = ( 201 ) 
(111) 
34 43 
34 53 
35 1 
35 16 
< o'p = (111) 
(110) 
92 49 
92 17 
91 59 
92 9 
l pr =(110) 
(201) 
52 28 
52 50 
53 0 
52 35 
Of the 38 angles compared in the second table, 32 show a change of angle, on 
passing from the potassium salt to the ammonium salt, in the same direction as is 
observed when rubidium or caesium replaces potassium. Of these 32 cases, 27 show 
larger changes than for the rubidium replacement, and 10 even larger ones than for 
the caesium replacement. 
Double Sulphates containing Copper. 
Replacement. 
Average change. 
Maximum change. 
K by Rb .. 
22 
/ / 
53 
K by Cs. 
47 
115 = 1 55 
K by NH 4 . 
39 
101 = 1 41 
The third small table shows that the average and maximum change of angle for the 
ammonium replacement is nearly as much as for the caesium replacement, both being 
twice as much approximately as for the replacement of potassium by rubidium. 
Cleavage. —The cleavage common to the series, parallel to 7 y {201}, is developed, but 
is not very facile. There is quite a good cleavage parallel to b {010}, and in this salt this 
cleavage is undoubtedly the better one of the two. The fact was confirmed on several 
crystals of different crops, and excellent images of the signal were obtained from the 
cleaved surfaces, at exactly 90 degrees from c faces subsisting on the fragments 
