June, 1921] 
MACDOUGAL WATER DEFICIT 
299 
which enter into nutritive solutions, as potassium, magnesium, sodium, and 
calcium, might find their chief importance in restricting, limiting, or de- 
fining hydration. Such an action is exerted by these bases in the form of 
hydroxides when tested at o.oi N. MacDougal and Spoehr"^ found later 
that the hydroxides of the strong metallic bases limit the hydration of agar 
according to their position in the electromotive series, the least swelling 
taking place under the action of the strongest base at concentrations of 
O.OI N, with the apparent exception of rubidium. Beginning with the 
strongest, the series runs K > (Rb) > Na > Li. The various effects of 
barium, calcium, and strontium are not so clearly determined, and the 
quantitative relations of these metals are not known definitely. Hydration 
values of agar at o.oi N were Sr(0H)2 = 815, Ca(0H)2 = 860, Ba(0H)2 
= 900. 
These concentrations are far beyond the actual range of conditions in 
the cell, however, and when reduced concentrations were used it was seen 
that hydration of agar in calcium hydroxide exceeds that in water at 0.0001 
N of the hydroxide, and this effect is also produced at 0.00001 N. 
Increase of hydration beyond that of water by dilute solutions of hydrox- 
ides of calcium, potassium, rubidium, potassium, sodium, and lithium, and 
excess values for aniline and ammonium hydroxides were obtained. 
It was also seen that the strongest of the bases, potassium, in the form 
of a hydroxide would increase the swelling of agar-albumin mixtures to a 
point beyond that taking place in water alone. 
The next logical step was to test the effects of salts of the common metals 
on swelling of the biocolloidal components. Here again the interesting 
fact was found that as chlorides, sodium and potassium at 0.001 M caused 
greater hydration of agar than water, the swelling being greater in the 
potassium. At 0.0001 M, sodium, potassium, magnesium, and calcium 
chlorides caused greater swelling than in water, the maximum swelling 
being in sodium, the next in potassium, and the least in calcium. 
When chlorides of sodium and potassium were tested in series as shown 
in tables i and 2, it was found that pentosan-albumin mixtures showed 
increased hydration in the potassium chloride only as indicated in the 
tables. 
Table i. Hydration of mixtures of agar s parts, gelatine 2 parts at 14° C. Plates 0.18 mm. 
in thickness; swelling of sections given in thickness and volume 
O.OI M 
0.001 M 
0.0001 M. 
Th. 
Vol. 
Th. 
Vol. 
Th. 
Vol. 
HCL 
KCl 
CaCl 
Water 
1,900 
920 
600 
2,015 
960 
2,270 
1,220 
1,025 
2,530 
1,345 
1,430 
2,440 
2,030 
2,200 
1,575 
2,640 
2,268 
2,330 
^ MacDougal, D. T., and Spoehr, H. A. The components and colloidal behavior of 
plant protoplasm. Proc. Amer. Phil. Soc. 59: 154. 1920. 
