22 ROYAL SOCIETY OF CANADA 
.09 cb.m, per hour, about 8 ¢.c. per second through each tube, or 8 cb.m. 
altogether in 3.7 days. 
When the current of air had been flowing for a definite number 
of days, usually 3, 4 or 6, the iron cylinders were removed and heated 
in succession to a dull red heat over a combustion furnace, and the 
expelled gases were collected in large vessels over water. 
The 660 grams of carbon gave off 15,000 c.c. of gases, and these 
were drawn in 18,000 seconds through three small glass tubes in series. 
each containing 7 grams of charcoal. The small tubes were heated 
over a bunsen burner, and the gases driven off were collected over water 
and introduced into the electroscope. Two or three hours later the rate 
of leak of the gold leaf was determined. A complete observation occu- 
pied about nine hours. 
The readings obtained were of the following nature :— 
Divisions per 
minute. 
I. Natural leak of the electroscope.. .. .. .. .. .065 
II. Obtained from tubes after 3 days rest.. .. .. 25 
III. Obtained from tubes after 3 days run (8 cb.m.) .65 
ITT.-IT. Due to emanation in 8 cb.m. of air.. .. .. .40 
A standard solution containing 10-° grams of radium was 
then placed in a flask and the air bubbled from it through the three 
iron tubes at the same rate and for the same time as before. 
IV. Due to the standard solution and all causes in III ad 
VERT M Duerto 10 "erames|radiqun te se) ie. Ae neuer 1.45 
Hence 10° grams of radium gave 1.45 D/m 
and 8 cb. metres of air gave .40 D/m 
therefore, 1 cb.m. of air contains the emanation from 
1 40 
le 
Ben (AS 
or 3.5X 101 grams of radium. 
This is the largest value obtained, the smallest being one-half as large. 
As further experiments are in progress, with various speeds of air 
currents, it is not advisable to assign a more definite value at present. 
Tn any case it is clear that the direct method, by charcoal absorp- 
tion, gives a value less than half that found by the active deposit 
method; and there are good reasons to expect this divergence in values. 
in the first place it seems clear, both from theory and experiment, that 
the amount of emanation in the atmosphere varies. The emanation 
