Oct., 1923] ROBBINS — ISOELECTRIC POINT FOR PLANT TISSUE 
423 
creases in weight showed that they were comparable in amount to those 
secured in the former experiment with the more dilute buffer mixtures of 
H3PO4 and NaOH. In the first four solutions, pH 54-5.6, the potato 
continued to gain in weight for the 48 hours. Solutions 5-10, pH 5.75-6.6, 
showed losses in weight between the 24- and 48-hour weighings. Again it 
was noted that in the solution of original pH 5.4 the change in weight was 
Table 4. Gain or loss in weight of 10 g. of potato-tuber tissue in 6,12, and 24 hours in 150-cc. 
quantities of buffer mixtures of 0.01 M KH phthalate and 0.01 M NaOH 
Sol. No. 
Initial pH 
pH 
after 
6 Hrs. 
pH 
after 
12 Hrs. 
pH 
after 
24 Hrs. 
Gain or 
Loss, 
6 Hrs. 
Gain or 
Loss, 
12 Hrs. 
Gain or 
Loss, 
24 Hrs. 
Ash, 
24 Hrs. 
g. 
g- 
g. 
g- 
I 
4.2 
4.6 
4.6 
4.6 
I.092 
— O.90O 
-2.183 
O.OIII 
2 
4.6 
4.8 
4-7 
4-7 
I.242 
-O.150 
“ 1-933 
O.OI49 
3 
4-9 
5-2 
5-2 
5 -o 
L 367 
0-575 
—1.408 
0.0217 
4 
5-5 
5-6 
5-5 
5-6 
I.4OO 
O.570 
-0.983 
O.O241 
5 
5.85 
5.85 
5-8 
6.0 
I.392 
O.942 
— 0.008 
O.O349 
6 
6.2 
6.2 
6.2 
6.2 
1-333 
0.800 
-0.492 
O.O394 
7 
6.2 + 
6.2 + 
6-3 
6.2 
1.442 
I.025 
—0.267 
O.0358 
8 
6-3 
6-3 
6.4 
6.2 
1.492 
1.142 
-0.050 
O.0314 
9 
6.9 
6.4 
6.4 
6.2 
1-433 
I.O33 
— 0.108 
0.0359 
10 
7.6 
6.5 
6.6 
6.2 
1.408 
0.925 
-0.150 
O.O383 
11 
Redist. 
H 2 0 
6.6 
6.2 
6-3 
5.8 
2.097 
2.008 
1-550 
O.0409 
least between the 24- and 48-hour weighings. In figure 3 the gains in 
weight at the end of 12 hours are plotted against the average pH of the 
solutions. If a smooth curve is drawn through these points, we have again 
a double maximum with a minimum between at a pH of 5.85. If all points 
were connected, a W-shaped curve with the peak at 6.05 wouid be obtained. 
Citrate—NaOH Series 
The buffer mixtures used in this series were prepared by mixing 0.1 M 
secondary sodium citrate and 0.1 M NaOH as proposed by Sorensen follow¬ 
ing the tables given by Clark (3), and diluting the solutions so secured either 
10 or 50 times. Redistilled water was used in preparing these buffer mix¬ 
tures. The calculated concentrations of the secondary sodium citrate and 
sodium hydroxide used in these two dilute buffer mixtures are given in 
table 1. 
In the first experiment the original buffer mixtures diluted 10 times were 
used. This was equivalent to mixing 0.01 M secondary sodium citrate and 
0.01 M NaOH. The potato was weighed at the end of 6, 12, and 24 hours. 
At the first weighing the solutions from 4 to 9 were slightly turbid due to 
the development of bacteria, while the rest were clear. The potato appeared 
to be in good condition. The bacterial development was about the same 
at the second weighing, but the potato was quite flaccid especially at the 
