190 
Walter Stiles 
butyrate, valerianate, salicylate, sulphate, thiosulphate, As 0 3 , B 4 0 7 
(the two silicate membranes were not examined in the case of the 
last four anions). The results with other ions are shown in Table XIII. 
Table XIII 
Permeability of Various Precipitation Membranes to Anions bound 
to Alkali Metals (K, Na, ?Li, NH 4 ) (p permeable, i impermeable). 
(Data from Walden) 
Anion 
A 
Membrane 
r 
po 4 
As0 4 
S 0 4 Cr 0 4 
p 2 o 7 
Oxalate 
Ferrocyanide 
Ferricyanide 
Cobaltocyanide 
Glue-tannic acid 
p 
P 
(Se 0 4 ) 
P 
P 
P 
Silicate 
P 
Ni 3 (CoCy 6 ) 2 
p 
P 
P 
P 
P 
i 
Ni 2 FeCy 6 
p 
P 
P 
P 
P 
i 
Co 3 (CoCy 6 ) 2 
p 
P 
P 
P 
i 
i 
Co 2 FeCy 6 
p 
P 
P (i) 
i 
i 
i 
Cd 3 (CoCy 6 ) 2 
p 
i (P) 
i 
i 
i 
Nickel silicate 
i 
i 
i 
i 
Cobalt silicate 
. 
i 
i 
i 
i 
Cu 3 (CoCy 6 ) 2 
i 
i 
i 
i 
i 
i 
Zn 2 FeCy 6 
i 
i 
i 
i 
i 
i 
Cu 2 FeCy 6 
i 
i 
i 
i 
i 
i 
In Table XIV 
are given Walden’s 
results as 
regards the per- 
meability of precipitation membranes to a number of positive ions 
bound (generally) to halogens. 
The significant fact to be noted from W T alden’s results is that 
these membranes form a perfectly regular series in regard to their 
permeability to the substances examined, glue-tannic acid being the 
most permeable, and allowing the passage of everything investigated 
except alkali tannates and halides of (?) cadium, zinc and manganese, 
while copper ferrocyanide is the least permeable, the other mem¬ 
branes being intermediate in their permeability. 
From these results and those obtained with a large number of 
acids, Walden concluded that the penetrability of substances depends 
not so much on the number and weight of the atoms composing 
their molecules, as on the nature and arrangement of the constituent 
atoms. Thus sulphate and thiosulphate have the same number of 
atoms in the molecule, but precipitation membranes are much more 
permeable to the latter than to the former. The same is the case with 
sodium acetate and sodium oxalate. In general, while both electro¬ 
lytes and non-electrolytes may be able to pass through a membrane, 
acids and salts containing at least one univalent ion diffuse through 
most easily. Potassium and ammonium chlorides, bromides and 
iodides pass through membranes with nearly equal ease. With other 
