EXPERIMENT STATION BULLETINS. 



665 



ence between the pure water and the highest concentration is 5.53°. 



p]xperinient 5. In this experiment an attempt was made to study the 

 influence of the salt solutions on the rise of temperature under practical 

 conditions. The experiment was performed by inserting into the ground 

 mercury thermometers to a deptli of three inches, and 12 inches apart, 

 and placing over an equal area, around each thermometer, equal quanti- 

 ties of water and some kind of salt solution. The general trend of the 

 different tests is well illustrated by the experiment below in which NaCl 

 and n„0 were used. Exactly 500 cc. of each was poured around each 

 Ihermometer. The solution was prepared by dissolving 100 grams of the 

 salt in one liter of water. 



TABLE 83.— EFFECT OF SOLUBLE SALTS ON THE RISE OF SOIL TEMPERATURE. 



It is evident that as in the preceding experiments with sand, the salt 

 solution has a predominate influence on the rise of temperature. It will 

 be seen that at 8 :10 when the maximum temperature was attained for 

 the day the soil treated with the salt solution is 6.70° F. warmer than 

 the soil treated with pure water. 



That the concentration of solution influences the rising of temperature 

 and that this degree of rising may be considerable is beyond any doubt 

 from the foregoing work. The question now is what factor or factors 

 bring about this result. From all evidence it appears to be due to the 

 diminution of evaporation of water by the higher surface tension and 

 lower vapor tension of the higher densities. If this be so then the sand 

 treated with the most concentrated solutions should contain at the end of 

 a certain period or at the time when the maximum temperature is at- 

 tained, a higher percentage of moisture than the sand to which was 

 added pure water or dilute solutions. The determination of the moisture 

 content of some of the lots of sand shows such to be the case. . These 

 moisture tests were made by pouring all the sand contained in the box 

 into a large pan thoroughly mixing it and taking composite sample 

 from the mass. The results obtained are given herewith : 



TABLE 84— MOISTURE CONTENT AT END OF EXPERIMENT. 



Name of solution. 



Per cent 

 moisture. 



H2O 



KHzPO* 

 K2CO3... 

 K2SO4... 



2.30 

 3.25 

 4.7 

 4.0 



It will be seen that the moisture content is higher in the sand treated 

 with the salt than with pure water, hence it supports the hypothesis. 



