RESEARCH METHODS IK STUDY OF FOEEST 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 McCool and Millar (131) is likely to be ineffective. Hibbard and 

 Harrington (120) 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 hooks 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 

 zero, and the lowering of the freezing point of the pulp was obtained by 

 subtraction. When determining the freezing poinl of distilled water an elec- 

 tric st'rring 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 ondercool about t", after which the beginning 

 <.f solidification was broughl 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 al si Imi [lately and soon 



camp to re t, after which the thermometer was tapped several times and the 



