71G STATE BOARD OF AGRICULTURE. 



These results show that at the optimum moisture content the rate of 

 solubility is slow and the extent of solubility is small, of all the natural 

 or untreated soils. Considei-ing first the rate, it is at once seen that the 

 depression rises only from about .008° to about .0\?>° in ten days to 

 about .035 °C in sixtj^ days. In some of the soils and especially in the 

 sands the rate is still slower. Considering next the extent, it is imme- 

 diately observed that the amount of material that went into solution is 

 comparatively small. The maximum depression at the end of sixty days 

 in any soil is only .037 °C or 925 parts per million of solution. In several 

 of the soils the quantity is still smaller and in the case of the sand and 

 peat it is less than 375 parts per million. 



Comparing now the total amount of material that went into solution 

 at the two different sets of moisture content it is seen that the quantity 

 is somewhat greater and, especially in some soils, at the water content 

 of supersaturation. Thus, at the high moisture content the freezing 

 point depression of soils Nos. 9, 11, 12, U, and 31 is .051°, .049°, .045°, 

 .460°, and .035 °C, respectively. While at the optimum moisture content 

 the depression for the same soil in the order named is .037°, .035°, .035°, 

 .037° and .027 °C, respectively. The difference, therefore, in some of the 

 soils, is as great as .014° depression in favor of the high moisture 

 content. 



The order of extent of solubility of the various soils is not exactly the 

 same at the two sets of moisture contents. In other words, the soils which 

 gave the largest solubility product at the high moisture content did 

 not do it also at the optimum moisture content. The deviation in the 

 order is not very great, but it cannot be stated that there is an absolute 

 correlation. 



Rate of Solubility of Natural or Untreated Soils Which Were Pre- 

 viously Washed Until All Their Free Soluble Salts Were Eliminated. 

 Ratio of Soil to Water was About 1 to .7 and Mixture Maintained at the 

 Temperature of 53 °C. 



In all of the foregoing series of exi)eriments the rate and extent of 

 solubility of soils under various conditions and treatments were meas- 

 ured at room temperature. Now it is known that temperature influences 

 solubility. Furthermore, the temperature of the soil under field condi- 

 tions changes very markedly during the various seasons of the year. It 

 appeared very desirable, therefore, to investigate the influence of tem- 

 perature upon the rate and extent of solubility. For this purpose two 

 sets of temperatures were used, 53 °C, and below freezing. The investiga- 

 tion at the temperature 53 °C will be considered first. The procedure 

 consisted of placing washed soils in the freezing point tubes, adding 

 water to them to bring up the water content to tlie raticui of 1 of soil to .7 

 of water, determining the freezing point, stopping the tubes with rubber 

 stoppers, and placing these tubes containing the soils in a constant tem- 

 perature oven whose temperature was maintained at about 53 °C. At 

 various intervals these tubes were taken out, opened, their contents 

 stirred and their freezing point depression determined again. In order 

 to prevent any pressure being produced by the raising of the temperature 

 the tubes were opend a few minutes after they were in the temperature 

 oven. The process of opening the tubes and stirring the contents also 

 tended to eliminate the accumulation of any gas that might be pro- 



