58 Physico-Chemical Properties of Vegetahle Saps [March, 



usual manner/ using a Freas conductivity celF having a cell con- 

 stant of 0.41 19, obtained by taking the specific conductance of o.i 

 N KCl as 0.01412 at 30°. 



D. Determination of the Depression of the freezing 

 POINT, The depression of the freezing point was carried out by 

 the well known Beckmann method, using the modifications we have 

 suggested (Gortner and Harris, 19 14), which make for more rapid 

 work. The freezing point of the sap from the proliferous mass 

 was determined immediately after that of the sap from the corre- 

 sponding ovary walls. All freezing points were corrected for the 

 concentration caused by the Separation of ice due to undercooling. 



A = A' — 0.0125 u^' 



where A' is the observed depression, u is the degrees of undercool- 

 ing and A is the corrected depression of the freezing point. 



E. Determination of the specific gravity. The specific 

 gravity at 20° of the plant sap was obtained by weighing in a small 

 pycnometer holding 5.6830 gm. of water at 20°. The maximum 

 error in the specific gravity determination is not greater than 

 + 0.0002. 



F. Determination of the concentration of the so- 



Wt solutes 



LUTES in the sap. The concentration of the sap ^^^ z was 



Wt. solvent 



determined by evaporating to dryness, at the temperature of a 



water oven, exactly 10 c.c. of the sap in a small weighing bottle. 



The weighing bottles were then placed in vacuum desiccators over 



conc. sulfuric acid and the desiccators exhausted to a pressure of 



less than 30 mm. Hg, and allowed to stand for at least 10 hours. 



They were then weighed. Drying at 105°-! 10° gives a smaller 



value for solids, but we believe that this is not caused by a further 



6 Cf. Abderhalden : Handb. d. Biochem, Arbeitsmethoden, I, 485-498, or any 

 good manual of physical chemistry. 



'' This type of cell is very well suited for rapid work. The electrodes are 

 held rigidly in place by small glass rods so that the cell may be shaken to remove 

 traces of moisture. The cell was frequently tested with o.i N KCl, but during 

 a period of nearly a year (during which time we have made some 1500 determi- 

 nations of electrical conductivity), the cell constant has not changed. Cleaning 

 the cell with chromic-sulfuric acid does not alter the cell constant. 



