444 BOTANICAL GAZETTE [DECEMBER 
solved in tooo gm. water=1 mole sucrose hexahydrate dissolved 
in 1000—(18X6), or 892 gm. water, and 2.085° (K,»,)=A due to 
1 mole dissolved in 892 gm. water. 
But in sample 13 the increase in A on addition of 1 mole sucrose 
(A.—A) was 2.339°, and 2.339°=A due to 1 mole dissolved in 
1.86X 1000 
2.339 
892—795 =97 gm.,=9.7 per cent. 
In laboratory practice it is most convenient to weigh out a fresh 
portion of the sap containing 10.0 gm. of water, add 3.422 gm. of 
sucrose, and redetermine the freezing point. The percentage of 
Excess A > 892 
observed A—sap A 
=795 gm. water; therefore the water bound per liter = 
bound water is then given by the formula: 
A,— (A+ K,,) 
water= 
or bound water RoR 
X 892. 
Comparing sample 13 with sample 16, it will be seen that whereas 
the percentages of total solids vary widely, the percentages of bound 
water are not greatly different. A reference to the values for 
viscosity and A will indicate at once the marked difference in the 
physical properties of these two saps, due to the large content of 
colloidal material in sample 16, a fact which is strikingly reflected 
in the percentage of bound water. Again, dialysis showed that 
material similar to sample 17 contained approximately twice the 
quantity of colloids as was contained in material similar to sample 
20, and these two samples differ widely in percentage bound water. 
These examples are cited to illustrate the application of the method. 
Discussion of the significance of the variations observed in the wheat 
varieties is reserved for a later paper on another subject. 
The percentages of bound water obtained with gum acacia sols, 
as shown in the table, increase regularly with concentration. In 
fig. 1 the percentage concentration has been plotted against the 
percentage bound water. The logarithms of these values have 
also been plotted in the same figure. It will be seen that both of 
these graphs suggest an adsorption curve. 
The advantages of sucrose as the solute in this method are as 
follows: (x) it is easily obtained in a high degree of purity; (2) the 
large molecular weight reduces errors in weighing; (3) its behavior 
