100 ROYAL SOCIETY OF CANADA 
containing the non-absorbing brick had a greater free volume than the 
tube containing -31 gms. of charcoal. 
It should be noticed that the greater the quantity of charcoal the 
greater must be the speed of air current to get any effect at all in the 
testing vessel. Thus, up to a speed of 0-5 c.c. per sec. there is prac- 
46e 
‘FO 

20 
18 
LOGARITHN OF 
OS 

1 2 3 
RECIPROCAL OF FLOW IN CC. PER SEC 
Fie. &. 
tically 100 per cent absorption by 5:86 gms. of charcoal, and up to a 
speed of 0-2 per sec. there is 100 per cent by 1:61 gms. 
EXPRESSION FOR THE ABSORPTION. 
Let i, be the ionization current in the testing vessel in the case of 
a non-absorbing substance, and i, the ionization current in the case of 

