PHYSICS: H. B. LEMON 
295 
nomena are to be regarded as saturated solutions of a rigid phase, carbon, in a 
fluid phase, gas. It suggests that repeated solution and subsequent evapora- 
tion, here taking the form of adsorption at low temperatures and outgassing 
at high, produces a gradual modification of the character of the carbon with 
respect to its fineness of division, something similar to precipitation occurring. 
Loss of activity seems difficult to account for on the first hypothesis. It is 
to be noted that permanent loss of activity can always be produced on any 
sample by heating to 1200°C. This is usually ascribed to a partial destruc- 
tion of porosity and has been observed before. Attempts to extract heavy 
hydrocarbons by the use of the lightest liquid solvents, hgroin alcohol and 
acetone were inconclusive. Considerable amounts of tarry material were 
removed, but not by the solvents directly. They distilled out during out- 
gassing after treatment with the solvent. This treatment in all cases causes 
temporary loss of activity which is renewed in the usual manner with re- 
peated use after low temperature outgassings. Experiments by others how- 
ever^ which have shown that activation is possible by other methods than the 
ones here outlined seems to favor the hydrocarbon hypothesis. 
Those other methods for activation of field material for the adsorption of 
complex vapors have been used in conjunction with the above described proc- 
ess. A comparison of material activated by use and low temperature out- 
gassings alone as herein described, with the most highly activated charcoals 
produced elsewhere under the conditions of these experiments is given in 
figure 6. The crossing of the curves may be very significant. The laboratory 
charcoal, R. 16, is less active initially but ultimately runs to lower values 
than the field material U. S. 4 and U. S. 6. The differences at either end are 
not large in comparison with the range of the phenomena discussed above. 
Experiments are in progress on saturation values for adsorptions of mix- 
tures of varied proportions. An hypothesis originally advanced by McBain^ 
that there is a distinction to be made between surface condensation and in- 
terior diffusion is also being subjected to experimental scrutiny with modern 
materials now at our disposal. Both of these lines of work it is hoped will 
shed light on the mechanism of the process. 
A more detailed account of this work will shortly appear in the Physical 
Review as a series of papers under the general title of Studies in Charcoal 
Adsorption. 
^ This article is published with the approval of Major General William L. Siebert, Director 
Chemical Warfare Service, U. S. A. 
2Shrader, Ithaca, N. Y. Physic. Rev., 12, 1918, (70). 
3Homfray, Liepzlg, Zs. Phys. Chem., 74, 1910, (139). 
^Dorsey, Easton, Pa., J. Ind. Eng. Chem., 11, 1919, (284). 
6 McBain, London, Phil. Mag., 13, 1909, (916). 
