RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 107 
the highest concentration of the cell sap, he was led to investigate 
this matter further. Finding nowhere any reference to experiments 
on the latent heat of vaporization of solutions, and believing that the 
conception of the fixed nature of that quantity for water was based 
upon the fact that the condensation of steam had always been em- 
ployed to determine it, he has been led to perform a number of ex- 
periments with solutions and with distilled water. 
The most important and convincing of these shows that at the 
respective boiling points of water, and various solutions up to the 
point of saturation (for sodium chloride), the latent heat of vapori- 
zation, determined directly by means of an electric heating element, 
is practically a constant, though perhaps varying inversely as the 
absolute boiling point. Thus'a saturated salt solution whose boiling 
point is 7° above that of water and whose osmotic pressure is theo- 
retically about 400 atmospheres, requires only 4 per cent less heat, 
per unit of water evaporated, than does pure water. This, however, 
does not solve the problem, as will be seen from the fact that when 
placed over a steam bath the saturated salt solution evaporates at 
a rate of less than 5 per cent of that for pure water. There is in the 
problem, therefore, very evidently some factor besides vapor pres- 
sures and latent heats of vaporization when an external supply of 
heat is concerned. It appears to be a matter of conductivity and 
possibly also of convection. Further investigation of the problem 
is urgently needed. 
'Method of determining freezing points. — Since, as has been stated, 
the treatment of the leaves of forest trees, especially conifers, is 
likely to present some complications because of the extreme dryness 
which they sometimes show, it is believed the whole-tissue method 
of MeCool and Millar (131) is likely to be ineffective. Hibbard and 
Harrington (126) are therefore quoted here on the process used by 
them and involving grinding of the frozen tissues. From this basis 
any investigator will certainly be able to devise modifications to suit 
his special conditions. 
The apparatus used in our tests was the Beckmann outfit ordinarily used 
for such work and described in books on physical chemistry, consisting of a 
Beckmann thermometer, freezing tube, outer jacket, and a battery jar con- 
taining the freezing mixture. The freezing point of distilled water was taken 
as zero, and the lowering of the freezing point of the pulp was obtained by 
subtraction. When determining the freezing point of distilled water an elec- 
tric stirring device was used consisting of battery, metronome, magnet, and 
platinum stirrer, but this was not employed in determinations made upon 
pulps. The pulp was allowed to undercool about 1°. after which the beginning 
of solidification was brought about by rotating the thermometer backward and 
forward a few times in the pulp. When the undercooled mass of pulp was 
thus disturbed the temperature began to rise almost immediately and soon 
came to rest, after which the thermometer was tapped several times and the 
