ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 11 
sulphide,?! however, give variety enough. The order of cations 
is Ce, In, benzidine, Al > new fuchsine, crystal violet > quinine > 
morphine, UO, Sr. Ca > Be, Zn, Ba > Ng > _p-chloraniline. 
toluidine > aniline > strychnine > guanidine > H > K> Na >Li. 
The organic cations come in where they please and play havoc 
with any rule as to valency. ‘The chlorides and nitrates give 
practically the same values, and the sulphates are not far out of 
line, though it seems probable that the restraining power of 
sulphate is rather greater than that of chloride or nitrate. The 
liminal values in gram atoms of the cation per litre are 0°0056, 
0:0066, 0°0086, 0-110, and > 0-250 for potassium nitrate, sulphate. 
formate, acetate, and citrate, from which one can deduce that the 
order of adsorption of anion is: citrate >acetate >formate > sul- 
phate > nitrate, chloride. It is a great pity that Freundlich did 
not try other combinations, such as barium acetate, for instance. 
From the experiments on hydrous ferric oxide,”* the order of 
adsorption of the precipitating anions appears to be Cr,0, > SO, 
> OH > salicylate benzoate >formate >Cl > NO; >Br >], while 
the order for the cations is: H>Ba>Mg>TIl, Na, K. The 
univalent ions do not all behave alike, and neither do the bivalent 
ones; but the upholders of Schulze’s law can comfort themselves 
with the fact that the two sets do not overlap except in the case 
of hydrogen. There is no such comfort in the case of albumin. 
I have shown”? that the probable order of adsorption of anions, 
so far as known, is: sulphocyanate, iodide > chlorate > nitrate > 
chloride > acetate > phosphate > sulphate > tartrate, the sulpho- 
cyanate ion being adsorbed the most and the tartrate ion the 
least. Here there is nothing even to suggest Schultze’s law, 
and the firm belief which most people have in Schultze’s law is 
probably one reason for the marked failure to account satis- 
factorily for the phenomena with albumin. With the cations 
albumin appears to be fairly orthodox, for the order of adsorption 
appears to be Th, UO, > Cu, Zn > Ca > Mg > Li>K,Na> NH 
though even here the lithium stands higher in the series than it 
has been found with other substances. 
While there is unquestionably a tendency for ions of a higher 
valence to be adsorbed more strongly than ions of a lower valence, 
the experiments which have been cited show that there are many 
exceptions, and that the fundamental rule is that the adsorption 
is specific both as regards the adsorbing substance and the ion 
adsorbed. 
Albumin is a specially interesting case because it is peptised 
readily by cations or anions. When it 1s negatively charged, as 
in a slightly alkaline solution, a strongly adsorbed anion will 
make it more negative and more stable. Consequently, precipita- 
tion by a sodium salt will be more effective the less readily the 
anion is adsorbed. On the other hand, in acid solutions the 
71 Freundlich, Kapillarchemie, 351 (1909). Freundlich and Schucht, Zeit. phy». 
Chem. 564 (1912). f SiS : 3 
72 eos ation, Hapillarohemie, 352, 358, (1909). Zsigmondy, Kolloidchemie, 18% 
(1912). Pappada, Zit. Kollvidchemie, 9, 233 (1911). 
73 Bancroft, Jour. Phys. Chem. 19, 352 (1915). 
