[BOYLE] TEMPERATURE AND VELOCITY OF GAS CURRENT 109 
atures of the charcoal. These curves are plotted with the actual read- 
ing of the manometer as abscisse, that is, without taking any account 
of possible changes of velocity of air flow caused by the necessary dif- 
ference in temperature of the parts of the circuit through which the air 
flows. 
If à, and 7, are the ionization currents in the testing vessel, at any 
given speed of air current, in the cases of non-absorption and absorption re- 
glee 
spectively, then from (5) the per cent absorption is given by 100 (= 
1 
These values, for the different temperatures, are plotted in fig. 11, 
which shows that the absorption increases as the temperature of the char- 
coal decreases. From (7) we have log = =—sJ,. = Applying 
; 
this result in the present instance, the curves of log = on - base, 
1 
for the different temperatures, should be straight lines. Fig. 12 shows 
this to be the case, except for low speeds of the air current, Since, the 
volume of charcoal was the same at all temperatures, the slopes of these 
lines are proportional to the coefficients of absorptions of the emanation, 
or to the absorptive power of the charcoal at the respective temperatures. 
Fig. 13, table 6, shows the way this power varies, the ordinates being 
proportional to the slopes of the logarithmic straight lines, and the 
abscissae denoting the temperatures. If the curve is continued to where 
it would probably meet the temperature axis, as ‘shown by the dotted 
portion of the curve, we find that s will be zero, 7.e., that the charcoal 
will not absorb at all, at 310° C. It may be noted that the curve is 
practically a straight line between —78° and 100° C.,Avhich means that 
the absorptive power of the charcoal decreases in a linear relation 
with increase of temperature. 
À Te 1, 

Plotting the percentage absorption, ( ) 100, on a temperature 
cal 
base, we get the curves shown in fig. 14, there being a definite curve for 
every speed of the air current. It can be seen that these curves are con- 
verging to meet the temperature axis at about 310°, again suggesting 
that at that temperature there would be non-absorption. Experiments 
are in progress to determine if this is actually the case. If this is the 
case, the question which will present itself for investigation is—does 
cocoanut charcoal at temperatures higher than 310° fail to absorb only 
the emanation of thorium, or is this true for some other or for all 
other gases? 
Experiments will also be made to‘ascertain if the absorptive power 
of charcoal depends upon the size of the grains which constitute its 
