EXPERIMENT STATION BULLETINS. 721 



Ivutio — ^ ^ 



1:7 .02;^ .011° .082° .052° .050° .010° .048° .013° .037° .010° .009° C. 



The further significant fact to be noted in table 2G is that even though 

 the solubility product is greatly rednced when the ratio of soil to water 

 is 1 to 5, yet an apparent eiiuilibriuni seems to be attained at the end 

 of about 30 days. This apparent equilibrium, however, is not attained 

 very fast but only slowly and gradually a- condition analogous to that 

 in the other series of experiments previously reported. 



It is to be concluded, therefore, tliat when the ratio of soil to water 

 is 1 to 5 respectively the rate of solubility is very slow, the extent ex- 

 tremely small, and much smaller than that at the ratio of 1 to .7 or even 

 at the optimum'moisture content. 



It would now be of interest to compare the amount of material that 

 went into solution at the optimum water content with that at the other 

 two water contents. These comparisons can be made in tables 22, 23 

 and 26. When the comparison is made it is seen that as a general rule 

 a slightly greater amount of material went into solution when the water 

 content was 1 of soil to .7 of water than it did at the optimum moisture 

 content, and the least amount went into solution at the water content 

 of 1 of soil to 5 of water. From these results it is evident that the effect 

 of the relative masses of soil and water finds a limitation in both direc- 

 tions. When the ratio of soil to water is decreased the solubility prod- 

 uct decreases, when, on the other hand the ration of soil to water is 

 increased beyond a certain point the solubility product is again de- 

 creased. 



The diminished solubility at the optimum or at any other low moisture 

 content would probably be expected. In the first place a large portion 

 of the moisture at the low water contents is unfree. In the second place, 

 water in the film form may not dissolve the solid material of the soil 

 as readily as the free and excess water. In the third place, the moisture 

 at the low water content is not so uniformly distributed in the soil as 

 at the high. 



Rate and Extent of Solubility of Natural or Untreated Soils Pre- 

 viously Washed and the Eatio of Water to Soil Was 1 to 5 and Mixture 

 Maintained at the Temperature of 53 °C. 



This investigation is precisely the same as the preceding one, except 

 that in this case tjie temperature was maintained at 53 °C. This was 

 accomplished by keeping the soils, in the closed tubes, in a constant 

 temperature oven of 53 °C. The object of this experiment was to study 

 the effect of high temperature upon the solubility of soils when the 

 ratio of soil to water was 1 to 5. The results procured are presented 

 in table 27. These results must be compared with those in table 24, 

 where the ratio of soil to water was 1 to .7 and the temperature at 53°, 

 in order to ascertain the effect of the relative masses of soil to water at 

 high temperature upon the solubility of soils. To facilitate this com- 

 parison the soils in both tables are given the same numbers. 



