558 Mr Campbell, The Radioactivity of Potassium, 
tables : the figures given are usually the mean of four successive 
observations. 
Whenever material from a new source was introduced, care 
was taken that it contained no radium or other active element, 
giving rays of a nature different from those of the potassium salts. 
For this purpose another set of measurements was made in which 
the material was covered with a layer of tin-foil thick enough to 
absorb all a rays. In no case was the proportion absorbed by the 
tin-foil different from that absorbed when a pure potassium salt, 
tested for radium by the emanation method, was used. It may 
be concluded, therefore, that all the activity measured was due to 
the active element of the potassium salts. 
The salts obtained commercially as “ pure ” were assumed to 
contain the theoretical amount of potassium. In most other cases 
the salts were analysed. These analyses were carried out in the 
agricultural laboratory by the cobalticyanide method, and I am 
deeply indebted to Prof. T. B. Wood for his kindness in having 
these estimations made. 
§ 3. Table I gives a summary of the chief observations. 
Table I. 
Material 
7o k 2 o 
Activity 
Activity of K 2 0 (calc.) 
k 2 so 4 (1) 
54 
87 
161 
(2) 
54 
87 
161 
(3) 
54 
86-5 
160 
(4) 
54 (?) 
85 
157-5 
(5) 
9-1 
14-4 
158 
(6) 
51-0 
82 
161 
(7) 
46-0 
75 
163 
(8) 
54? 
87-5 
162 
KC1 (1) 
63T 
102 
162 
(2) 
631 
102 
162 
(3) 
63-1? 
100 
159-5 
kno 3 (1) 
46-5 
72-5 
156 
(2) 
46-5 
70 
151 
IvCN (impure) 
57 
103 
181 
KI 
28-2 
39-5 
141 
K . C 2 H s O, 
48-5 
66 
136 
k 2 co 3 
68 
103 
152 
KC10 3 
38-4 
63 
167 
K. 2 S0 3 (impure) 
56-3 
87-5 
155 
Sylvine (IvCl) 
62*5 
102 
163 
‘Muriate of Potash’ 
51 
82 
161 
Ivainite 
16 
22-5 
141 
