28 GENERAL AND PHYSICO-CHEMICAL. 



always >1. (If n = l then the formula would be ~=k and we^would be dealing 

 with a so-called solid solution.) 



APPLEYARD and WALKER 1 have studied the adsorption of organic 

 acids from aqueous and alcoholic solutions by means of silk; the divi- 

 sion was found to correspond to the above formula for adsorption. 

 FREUNDLiCH 2 has also carefully tested the adsorption of crystalloids 

 by carbon. From these experiments it was shown that the equilibrium 

 could be quickly attained from both sides, i.e., that the process was readily 

 reversible. The above-given formula was found sufficiently accurate 

 for the case where only the total quantity of the dissolved (to adsorb) 

 substance varied. The series in which the organic acids were adsorbed 

 by silk, as found by APPLEYARD and WALKER, were pratically the same 

 as with carbon. The influence of temperature was slight. 



According to KtisTER, 3 the combination between starch and iodine 

 is to be considered as an adsorption compound, and BILTZ 4 finds for the 

 division of As2Os between iron hydroxide (1) and water (2) the for- 

 mula =0.631. 



C2 



The theoretical foundations for the adsorption phenomenon are 

 not especially clear. Generally the adsorption is considered as con- 

 nected with segregation and surface tension phenomenon. At the con- 

 tact surface between a solid body and solution a surface tension exists 

 which is considered as positive, i.e., this attempts to diminish the 

 contact surface. The surface energy used thereby tends to be a min- 

 imum potential energy. As the product from size of surface and surface 

 tension are the same, and as the first cannot change, the surface energy 

 can only be diminished by a reduction of the tension. If, therefore, 

 the tension is diminished by increasing the concentration of a sub- 

 stance dissolved in a fluid, then this substance tries to collect itself 

 at the surface in greater concentration than in other parts of the fluid 

 (OsTWALD, 5 FREUNDLICH 6 ) . In regard to the surface tension of solid- 

 fluid we only know that it is positive, but can otherwise show great 

 differences (OsTWALD, 7 HULETT S ). According to this theory the facts 

 are that certain solid substances possess the ability of adsorbing dis- 



1 Journ. Chem. Soc., 69, 1334 (1896). 



2 Ueber die Adsorption in Losimgen, Leipzig (1906). 

 8 Ann. d. Chem. u. Pharm., 283, 360 (1894). 



*Ber. d. d. chem. Gesellsch., 37, 3138 (1904). 



Lehrb. d. allg. Chem., 2. Aufl., 2. Bd., 3. Teil, 237 (1906). 



8 Ueber Adsorption in Losungen, 50-51. 



'Zeitschr. f. physik. Chem., 34, 495, 1900. 



Ibid., 37, 385 (1901). 



