8 REPORTS ON THE STATE OF SCIENCE.—1918. 
suspended particles will be electrically neutral. This can be done 
by adding an electrolyte with a readily adsorbed anion. Since this 
is a matter of selective adsorption, the concentration of the added 
anion necessary to cause an adsorption equivalent to the hydrogen 
adsorption will vary with each anion. To put the matter more 
generally, the amount of an electrolyte necessary to precipitate a 
colloidal solution will vary with the nature of the cation, the anion, 
and the dispersed phase. While it is generally true that an ion of 
higher valance will be adsorbed more strongly than one of lower 
valence, this so-called law of Schulze® is only a first approximation 
and should be considered only as a guide. 
That some univalent ions are absorbed more strongly by some 
substances than some bivalent or trivalent ions is shown clearly in 
data by Odén on colloidal sulphur“, given in Table I. In the second 
column are the liminal concentrations necessary to coagulate 
the sulphur, given in gram atoms per litre of the cations; in the 
third column are given the reciprocals of those values, the so-called 
atomic precipitating powers. 
Tase [. 
Coagulation of Sulphur at 18°-20°. 
Liminal value gram-atoms |Atomic precipitating power 
Salt. Cations per litre. of cation. 
HCl 6 0°16 
LiCl 0°913 1-1 
NH,Cl 0°435 2°3 
(NH,).S0, 0°600 1:7 
NH,NO; 0°506 2°0 
NaCl 0°153 6-1 
Na2SO, 0:176 Bry 
NaNO; 0:168 6-1 
KCl 0°021 47°5 
K.SO, 0-025 oon7 
KNO; 0°022 45°5 
RbCl 0-016 63 
CsCl 0-009 108 
MgSO, 9° 0093 107°5 
Mg NOs)» 0-0080 125 
CaCl, 0°0041 245 
Ca(NO3)» 0-0040 247 
Sr(NO3)» | 0°0025 385 
BaCl, i 0°0021 A475 
Ba(NOs)» 070022 461 
ZnSO, 0:0756 13°2 
Cd(NO3)> 0-04.93 20°3 
AIC]; 0-0044 227 
CuSO, 0:0098 102 
Mn(NO3)» 0:0096 105 
Ni(NO3)o 0-04.46 22-4 
U0.(NOs)» 0°0137 — 73 
8 Jour. Prakt. Chem, (2), 25, 431 (1882) ; 27,320 (1884). Bancroft, Jour. Phys. 
Chem., 19, 364 (1915). : 
54 Der Kolloide Schwefel, 156 (1912). 
I 
