1918-19.] The Adsorption Isotherm at Low Concentrations. 53 
the first in the c axis. Such a curve has apparently been obtained by 
Trouton,* as also have curves entirely above the c axis, where u 0 is positive 
initially but w 0 negative near c = l, though his interpretation of the curves 
is not on the lines here indicated. Curves of the type shown in fig. 1 have 
been obtained by the author and others, as will now be discussed. 
Schmidt *j* examined the adsorption by charcoal of acetic acid in fairly 
concentrated aqueous solutions. In his calculations he made the assump- 
tion that the mass of the solution remained constant even when several per 
Fig. 1. Fig. 2. 
cent, as acetic acid was being positively adsorbed — apparently on analogy 
with the usual constant volume assumption implied in the formula 
a = v(c 0 -c). 
He thus obtained neither u 0 nor, as he believed, u, but the value m(c 0 — c) 
corresponding to u 0 {l — c). The (u 0 (l — c), c) curve showed a maximum of 
u 0 ( 1 — c), which Schmidt assumed to indicate a saturation of the adsorbing 
surface for c — 1. Schmidt has now abandoned J the formula he proposed 
to express his supposed results. 
The author § showed that in the case in question u Q (l — c) passed 
* B.A. Reports , 1911, p. 328. 
f Zeits. /. physik. Chem. (1910), lxxiv, p. 689. 
§ Medd.f. K. Vet. Akad. N obelinstitut (1913), ii, 27. 
t Ibid. (1916), xci, p. 103. 
