Apr. IS. 1920 Effect of Calcium Sulphate on Solubility of Soils 49 



The effect of the calcium sulphate on the rate of formation of soluble 

 salts in the soils investigated is appreciable. According to the data set 

 forth in Table I, as well as other data not recorded, the reaction is rather 

 gradual and prolonged. Of course the initial concentration of the solu- 

 tions of the treated soils was high, and it is possible that this influenced 

 the rate of changes which afterwards took place in the mass. 



It was considered advisable to wash the soils until the concentration 

 of the solution in the soils was at a very low point. This was done, and 

 the series of tests with washed soils was carried on at the same time and 

 under the same conditions as the previous one. The results obtained 

 are presented in Table II. An examination of this table shows that the 

 residuary effect of the calcium sulphate on the rate of formation of soluble 

 substances in the soils is remarkable. The changes in the concentration 

 of the soil solution did not all take place at once but continued for a num- 

 ber of days. 



Table II. — Effect of calchim sulphate on the solubility of washed soils held at high water 



content for various periods 



Soil 

 No. 



Condition of soil. 



Freezing-point depressions. 



After 2 

 days. 



After 4 

 days. 



After 6 

 days. 



After 8 

 days. 



After 10 

 days. 



After 3c 

 days. 



Treated. .. 

 Untreated 

 Treated. .. 

 Untreated 

 Treated... 

 Untreated 

 Treated. .. 

 Untreated 

 Treated... 

 Untreated 

 Treated. . . 

 Untreated 



"C. 



o. on 



.003 



. 002 

 . 000 

 . 000 

 . 002 

 . 000 

 . 000 

 . 001 



.003 



. 000 



.008 



"C. 

 0.015 

 .COS 

 .005 

 . 004 

 . 004 

 . 004 

 .005 

 . 002 

 .015 

 . 002 

 .008 

 . 012 



"C. 



o. 030 

 .008 

 . 012 

 .005 

 . 010 

 . 006 

 .018 

 . 004 

 .028 

 . 004 

 .013 

 . 012 



"C. 



D. 044 



. on 

 . 024 

 . 007 

 . 016 

 . 007 

 . 022 

 . 006 

 . 042 

 . 006 

 . 014 

 .018 



"C. 



3. 071 

 .013 



•057 

 . 009 

 .028 

 . 009 

 .058 

 . 010 

 .052 

 . 012 

 . 024 

 .024 



°c. 



o. lOI 

 . 026 



■ -073 

 . on 

 .066 

 . 014 

 . 184 

 . 017 

 . 070 

 .018 

 .098 

 .032 



A clay loam soil was treated with the calcium-sulphate solution, 

 washed, and let stand 30 days at the high water content, again washed 

 until the freezing-point lowering of the solution in the soil was 0.005° C, 

 and again let stand 30 days. At the end of this period the freezing- 

 point lowering of the control or untreated soil was 0.040°, and that of the 

 treated soil was 0.102°. The residuary effect of the treatment is quite 

 persistent. 



Another series was run in which the water content of the washed soils 

 was lower, or approximately the so-called optimum point. The con- 

 centration of the solution in the soil was not determined until the 

 end of a 30-day period. At that time the freezing-point lowerings of 

 the soils were great and not strikingly different from those of the high 

 water series. The results of this experiment are given in Table III. 



