Nov., 1921] 
RABER PERMEABILITY 
469 
It is to be noted that the two curves are similar. The ferrous curve 
Hes a Httle below the ferric curve. Even though the two are of the same 
acidity, the ferric causes a greater rise in resistance at the start than the 
ferrous solution. The additional positive charge on the cation seems to be 
the chief cause of the difference between these two solutions. 
In order to see how much of the action of these salts is due to the high 
acidity, a third set of experiments was performed using 0.28 M FeCU of 
the original pH (about 4). This concentration is the equivalent of a 0.0001 
N HCl solution and, as mentioned above (2), this degree of acidity has 
been found to have no appreciable effect upon the permeability of Laminaria. 
The results of these three experiments are shown below and in figure 2, C. 
Time in Percentage of Probable Error 
Minutes Original Resistance of the Mean 
2 112 1% 
5 116 2 
10 114 4 
20 109 3 
40 85 4 
60 67 7 * 
80 51 10 
100 40 10 
The tissue here retains its original color and (as shown by the table and 
figure) the increase in resistance takes more than twice as long to reach a 
maximum. The general behavior and appearance of the tissue is very 
different from that in the two previous cases, and has in common with 
them only the initial increase followed by a decrease in resistance. The 
greater rise in the ferric chloride is not due to the concentration, since 
the ferric chloride is really less concentrated than the ferrous, the former 
being 0.20 M and the latter 0.23 M. 
The conclusion would seem to be that in the case of curves A and B 
the primary factors are the ferric, ferrous, and chlorine ions while the 
hydrogen ion plays a subordinate role. The acidity causes the maximum 
rise to be arrived at much earlier and causes the extremely rapid fall. The 
valency of the cation, however, determines largely the height to which the 
resistance rises. 
Summary 
1. Chromium has a different initial effect upon the permeability of 
Laminaria depending upon whether it occurs in the cation or in the anion 
of a salt. If it is in the anion, the first effect is a decrease in resistance, and 
if in the cation, an increase. 
2. Ferric chloride causes a greater increase in resistance than ferrous 
