1918-19.] The Adsorption Isotherm at Low Concentrations. 51 
substances by Freundlich,* shows that of forty-four values, in only one 
case is the value 0‘50 exceeded — namely, 0*52 with mercuric chloride and 
blood charcoal in water. Numerous other cases in recent work indicate 
that the value 050 is not exceeded, and this suggests 
1 
2 
as the limiting 
value of - when c = 0. 
n 
It is, however, conceivable that at still greater 
dilutions than those examined the value of — approaches unity, as with 
gases. It is further to be noted that while in the cases mentioned c may 
be small, the concentration in the adsorption layer is still not small. Thus, 
using the fact that w — 0 69 when c is small, we have from Table III above 
the values of — given in Table IY. 
w & 
We may expect to obtain smaller values of n 0 for a given c when 
Table IY. 
c 
u 0 
u 
w 
0*0000122 
0-0042 
0-006 
347 
73 
•Oil 
•00159 
r- 
• 9 
•026 
we increase the temperature (on analogy with gaseous adsorption), and 
Freundliclrj* gives (log c, log a) curves for aqueous acetic acid and charcoal 
where the gradient is 045 at 0° C., 0*6 at 50°, and 0‘8 at 94°. Again, 
Georgievics and Dietl J in studying the time rate of adsorption from 
aqueous solution of acids by wool at 20° C. give figures which indicate a 
gradient of 0*70 with acetic acid and 0*75 with propionic acid. Ritzel § 
shows that the adsorption of uranium-X by charcoal appears to obey 
Henry’s Law, and this is confirmed by Freundlich and Kaempfer. || In 
the case of adsorption of metallic salts by silica, Schmidt IF showed from 
his own and from van Bemmelen’s** results that Henry’s Law held. The 
figures in Table Y show this in the case of sodium chloride. The author’s 
figures *|**|* in Table YI for aqueous solutions at 25° C. and blood charcoal 
bear on the question. It will be noted that here u 0 and therefore ^ are 
* Kapillarchemie (19 09), p. 150. f Loc. cit ., p. 171. 
I Zeits.f. physik. Chem. (1914), lxxxvii, p. 669. § Ibid. (1909), lxvii, p. 732. 
|| Ibid. (1915), xc, p. 681. IF Ibid. (1895), xv, p. 56. 
** Jour.f. prcikt. Chem. (1881), xxiii, p. 324. ft Trans. Farad. Soc. (1914), x, p. 155. 
