A METHOD FOR ESTIMATING HYDROPHILIC COLLOID 
CONTENT OF EXPRESSED PLANT 
TISSUE FLUIDS! 
ROBERT NEWTON AND ROSS AIKEN GORTNER 
(WITH ONE FIGURE) 
In the preceding paper by GoRTNER and HorrMAn? it was 
pointed out that studies of the physico-chemical properties of plant 
saps which include only measurements of the osmotic pressure, 
electrical conductivity, and H-ion concentration, leave out of 
account the very important influence on physical properties exerted 
by sap colloids. By the introduction of the refractometer as a 
part of the field laboratory equipment, these workers have shown 
it possible to make rapid and accurate determinations of the 
moisture content of the plant saps. Utilizing the additional data 
thus made available, a simple method has been devised which 
appears to give a relative measure of the content of hydrophilic 
colloids. 
The freezing point depression of the freshly expressed plant 
juice is first obtained. Then, having determined the total solids 
by the refractometric method, a quantity of sucrose just sufficient 
to make a molar solution in the total water present is added. The 
freezing point depression is again determined, and is usually found 
to have increased more than the theoretical amount. 
The values for the excess depression recorded in this paper have 
been based on the assumption that sucrose forms the hexahydrate 
in solution. The evidence for this has recently been discussed by 
SCATCHARD,’ who also contributed additional data. In prelimi- 
nary experiments with pure sucrose dissolved in distilled water, 
freezing point depressions were obtained slightly in excess of those 
* Published with the approval of the Director, as Paper no. 323, Journal Series, 
Minnesota Agricultural Experiment Station 
? GorTNER, R. A., and Horrman, W. F., Determination of moisture content of 
expressed plant tissue fluids. Bor. Gaz. 74:308-313. 1922. 
3 ScaTcHARD, G., The hydration of sucrose in water solution as calculated from 
vapor-pressure measurements. Jour. Amer. Chem. Soc. 43:2406-2418. 1921 
Botanical Gazette, vol. 74} [442 
