Vol. 6, 1920 
CHEMISTRY: HARKINS AND EWING 
55 
of charcoal at low pressures is greatly increased by repeated outgassing or 
by treating with the vapors or gases to be adsorbed several times between 
outgassings. Harned has noticed that in the latter way the speed of 
adsorption is increased, but" the effect noticed here is on the equilibrium 
value. One gram of 750 minute charcoal, according to the ordinary 
chlorpicrin test, was outgassed, treated with benzene vapor, and then 
outgassed a second time. The volume of the whole apparatus was 2,200 
cu. cm., and was filled at 24° with benzene vapor at a pressure of 1.5 mm. 
On opening this volume to the one gram of charcoal, the pressure fell in 
12 hours to 0.00002 mm., or to less than one seventy thousandth of the initial 
pressure. The long time necessary was due to the fact that the equilibrium 
between the outside and inside of the lumps of charcoal is adjusted very 
slowly, since the diffusion is very slow. In a similar manner a pressure 
of 5.13 mm. was reduced to 0.00004 mm. In these experiments the charcoal 
was also at 24° C, so they illustrate the extremely great effect of the char- 
coal surface in increasing the life of the molecule^^ on the surface above 
what it would be on the surface of the liquid. In the second of these two 
experiments about one-tenth of the surface of the carbon was covered by 
molecules of benzene, provided the above estimates of the area of the sur- 
face are correct. On account of the great differences in the curvature of the 
surfaces of the pores, the different molecules are held by widely varying 
forces. 
The apparatus first used in this work was similar to that described by 
Lemon, but it was soon found that more rapid work could be done in 
an apparatus in which there are no stopcocks. Our work is the first which 
relates to the volume of different liquids taken up by charcoal. In addi- 
tion to papers already cited, reference should be made to a paper by 
Chaney^^ on the activation of carbon, to papers by Langmuir^^ and by 
Harkins and his co-workers^^ on the theory of surfaces and adsorption, 
and to papers on adhesion by Harkins. Thanks are due to Dr. Chaney 
for the preparation for special charcoals, and to the Gibbs Fund of the 
National Academy of Sciences for a grant which enabled us to purchase 
the vacuum apparatus. 
1 Titoff, Zs. physik. Chem., 74, 1910 (641). 
2 Baerwald, Ann. Physik, 23, 1907 (84). 
3 Miss Homfray, Zs. physik. Chem., 74, 1910 (129). 
* Bridgman, an extensive series of papers in Proc. Amer. Acad. Arts Sci., especially 
49, 1913 (No. 1). 
s Richards, /. Amer. Chem. Soc, 38, 1916 (989). 
6 Williams, Proc. Roy. Soc. Edinburgh, 38, 1917-8 (23); 39, 1918-9 (48); Proc. Roy. 
Soc. London, A 96, 1919 (287 and 298). 
^Langmuir, (a) Met. Chem. Eng., 15, 1916 (468); (6) /. Amer. Chem. Soc, 39, 1917 
(1848); (c) Ihid., 40, 1918 (1361). 
8 /. Russ. Phys. Chem. Sec, 47, 1915 (805). 
9 Donny, Ann. chim. phys., 16, 1846 (167) ; Berthelot, Ihid., (3) 30, 1850 (232) ; Moser, 
Ann. Phys., (2) 160, 1877 (138); Helmholtz, Gej. .46/?., 3, 1887 (264) ; Worthington^ 
