1922] GORTNER & HOFFMAN—MOISTURE CONTENT 3I1 
happened to the duplicate set being dried either over sulphuric 
acid or in the vacuum oven. 
The tissue fluids were obtained by means of a specially con- 
structed press bowl, and a hydraulic press, after the tissue had been 
rendered permeable by a preliminary freezing of the tissue for at 
least eight hours, following the procedure recommended by GoRTNER 
and Harris (1) and used in all of the previous work. All saps were 
centrifuged perfectly clear from suspended débris. We have 
included in the table values for A, the depression of the freezing 
point (corrected for under cooling), and the “‘average molecular 
weight’? of the solutes. 
Certain of the samples (nos. 9-14 and 17-21) were collected for 
another purpose by Mr. RoBertT NEWTON, and the significance of 
the various values will be discussed by him in a later paper. It is 
sufficient for our purpose to point out the difference between nos. 
- Ir and 14. We have here two wheat saps differing approximately 
3 per cent in the freezing point depression (and consequently in 
osmotic pressure), and at the same time differing by nearly 300 
per cent in total solids. This difference can only be due to a differ- 
ence in colloidal content, a fact that has been proved by NEwTon, 
using several other methods. Had we been concerned only with 
determinations of osmotic pressure, electrical conductivity, and 
hydrogen ion concentration, we might have concluded that these 
saps possessed practically identical physico-chemical, properties, 
whereas such a conclusion is far from the truth. 
Sample no. 21 is a wheat sap dialyzed completely free of sugar 
and electrolytes, and represents the non-dialyzable colloidal mate- 
rial. It will be noted that the refractometric method measures 
this colloidal material quantitatively. Newton recently had 
occasion to prepare, in this laboratory, gum acacia sols containing 
I, 2, 3, 5, 7, and 10 per cent of highly purified gum acacia, and refrac- 
tometric readings for total solids on the resulting solutions gave 
values corresponding with those of the weighed gum acacia which 
had been added to make the sols. 
* Calculated by aid of published tables. Cf. Harris, J. A., and GorTNER, 
Tables of the relative depression of the freezing point, 1860/A, to facilitate the 
calculation of molecular weights. Biochem. Bull. 3:259-263. 1914. 
