PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 6 FEBRUARY 15. 1920 Number 2 
AN APPARENT HIGH PRESSURE DUE TO ADSORPTION, THE 
HEAT OF ADSORPTION, AND THE DENSITY OF GAS- 
MASK CHARCOALS 
By William D. Harkins and D. T. Ewing 
Kent Chemical Laboratory, University op Chicago 
Communicated by J. Stieglitz, December 27, 1919 
A knowledge of the volume of the pores, and of the density of the active 
carbon in gas-mask charcoal, is of importance in connection with the 
working out of a theory in regard to the efficiency of charcoal as an ad- 
sorbent of gases, so the problem of the determination of the pore volume 
was given to us by the National Research Council in connection with the 
work of problem 108. We have discovered that factors which have hither- 
to been unsuspected complicate such a determination, the interesting new 
phenomenon being that the volume of the liquid absorbed depends upon 
the physical properties of the liquid. Thus it has been found that the 
volume of water or of an organic liquid taken up by a definite weight of 
any charcoal which is very efficient as an adsorber of gases, increases as 
the compressibility of the liquid increases, or as either the viscosity or the 
surface tension decreases. This effect decreases as the adsorptive capacity 
decreases, and entirely disappears when the charcoal becomes valueless 
as a gas adsorbent. 
While effects of the same general order were found whether the charcoal 
was put in the liquid directly from the canisters or from the bottles in which 
it was stored, or only after an extensive "outgassing" or heating and pump- 
ing out of the gases contained in it, concordant results were obtained only 
by the latter procedure. This is a well-known method for cleaning the 
surface of the charcoal, and the only new features introduced were those 
which concerned the completeness of the outgassing. The tube containing 
the charcoal was first exhausted by a rapid mercury condensation pump, 
and then heated up very slowly in vacuo until the temperature finally 
reached 600° C, keeping the pump running. The heating and evacuating 
usually continued for two days, though this time varied greatly with the 
nature of the charcoal, and was only ended when the pressure in the sys- 
tem fell to one ten-thousandth of a millimeter at this high temperature, 
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