Apr. IS. 1920 Effect of Calcium Sulphate on Solubility of Soils 53 



containing 0.25 and 0.5 per cent calcium sulphate. It should be borne 

 in mind, however, that the method of treating the samples was quite 

 different from that in the experiment here reported. Several investi- 

 gators have also reported a slight stimulation in ammonia production as 

 a result of treatment with small amounts of calcium sulphate. In none 

 of these experiments, however, were the soils thoroughly washed after 

 treatment with the sulphate, and consequently it does not seem to be 

 justifiable to make direct comparisons with our results. 



At the expiration of 30 days the concentration of the soil solution of 

 the samples maintained at the high water content was determined by 

 thoroughly stirring the sample, withdrawing a portion to a freezing- 

 point tube, and making the determination in the usual manner. Suffi- 

 cient water was added to the samples maintained at the low moisture 

 content to bring them up to that of the corresponding samples maintained 

 at the high water content. The results of these determinations, together 

 with the parts per million of soluble material, are presented in Tables 

 VII and VIII. 



Table VII. — Effect of calcium sulphate on the solubility of soils held at high water con- 

 tent for JO days 



Soil 

 No. 



Treatment. 



Freezing- 

 point 

 depressions. 



Soluble 

 material. 



Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 



"C. 



o. 101 

 .026 



• 073 



• oil 

 .066 



. 014 

 .184 

 .017 

 .070 

 .063 

 .098 

 . 042 



p. m. 



2,525 



650 



1,825 



275 

 1,650 



350 

 4,600 



425 

 1,750 

 1,575 

 2,450 

 1,050 



Table VIII. — Effect of calcium sulphate on the solubility of soils held at low water con- 

 tent for 20 days 



Soil 

 No. 



Treatment. 



Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 

 Calcium sulphate 

 No treatment . . . 



Freezing- 

 point 

 depressions. 



•c. 



O. 103 

 .015 

 .085 

 . 010 

 • III 

 .013 

 .163 

 . 007 

 .099 

 .023 

 . 096 

 .023 



Soluble 

 material. 



P. p. m. 



2,575 



375 

 2,125 



250 

 2,775 



325 

 4i075 



175 

 2,475 



575 

 2,400 



575 



