THE EFFECT UPON PERMEABILITY OF (I) THE 
SAME SUBSTANCE AS CATION AND ANION, 
AND (II) CHANGING THE VALENCY 
OF THE SAME ION 
Oran L. Raber 
(Received for publication April 6, 192 1) 
L The Effect of the Same Substance as Cation and Anion 
In a recent paper (i) facts were presented which indicate that polyvalent 
cations do not cause an increase in the resistance of Laminaria if they are 
combined with polyvalent anions, and it seems natural to suppose that the 
difference between the action of a salt with a bivalent cation and a mono- 
valent anion, e.g., MgCU, and one with a bivalent cation and a bivalent 
anion, such as MgS04, is due to the extra charge on the anion. Cations 
seem to cause an increase in resistance and anions a decrease. In MgCl2 
the action of the cation is dominant; in MgS04, the action of the anion. 
If this effect is due to electrical charge, we may ask what will happen if 
the same ion is used as cation and as anion. This problem seems at first 
glance to present great difficulties because it is necessary to work with 
solutions which are not strongly acid or alkaline. Certain elements (such 
as aluminum, arsenic, chromium, etc.) exist both as cations and as anions, 
but they are very weak acids or bases and solutions of their salts are not 
neutraL 
The difficulty may be surmounted in a measure, however, by adding 
enough acid to the alkaline solution to bring its pH value down to that of 
the acid solution. If necessary the conductivity may be increased by 
mixing with a neutral salt (e.g., NaCl). 
For this purpose, chromous chloride, sodium chromate, chromic acid, 
and sodium chloride were used. The chromous chloride is not soluble 
enough to make the conductivity equivalent to that of normal sea water, 
and in order that the osmotic pressure of the sea water (with which the 
solution is compared) should not be too low, the chromous chloride was 
mixed with sodium chloride. The final solution was then composed of 
50 percent chromous chloride 0.61 M and 50 percent sodium chloride 0.52 M. 
This mixture has greater electrical resistance than sea water and has a pH 
of about 4.5 as determined by the hydrogen electrode. 
When tissue is transferred to this mixture from diluted sea water of the 
same conductivity, the following changes in resistance are observed (see 
fig. I. A): 
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