267 
about 300 times that of uranium, was dissolved in 250 cm? of hy- 
drochlorie acid (about 8°/, eoncentration). The solution was evapo- 
rated on the water bath to about 100 cem. When ammonia was 
added to the solution, a reddish- brown substance (probably hydr- 
oxide) was precipitated. The precipitate eollected on a filter paper, 
was dried as quiekly as possible and then its activity was measu- 
red. The filtrate was then evaporated to dryness, and when ammo- 
nium salts were driven off by ignition, a small amount of a brown 
black residuum was left behind on the dish. On raising this to 
a red heat the colour of the residue changed from black to white. 
This residue was intensely active compared with the weight. Im- 
mediately after the dish was cold the activity of the residue was 
measured and was found to decrease slowly with the time accor- 
ding to an exponential law. In the same period the actinium which 
by precipitation had been rendered almost inactive recovered its 
activity, the recovery eurve being complimentary to the curve of 
decay. 
From analogy to ThX, which so closely resembles in radio- 
active properties, the active substance separated from actinium will 
be termed Actinium X (AcX). 
The results of one of the series of experiments are given in 
table I and graphically represented in Fig. 1. In table I the first 
column gives the days measured from the time of separation; the 
second column gives the activity. The activity of AcX is expressed 
as a percentage of the initial activity, the maximum activity soon 
after seperation being taken 100. But for the actinium (deprived 
of AcX) the final value is taken 100. 
Table I. 
t in days Activity t in days Activity 
0:25 875 01 5:25 
0.9 100 0:7 922 
19 92:6 1 16:7 
30 86:0 Zul 240 
4:0 815 357 29:6 
59 72:6 57 39:8 
69 70:7 6:7 48:0 
89 59:2 8:7 52:5 
