54 Journal of Agricultural Research voi. xix, no. a 



The total quantity of soluble material formed during the 30 days does 

 not coincide with the amount of the carbon dioxid produced. The data 

 show the treated samples to contain many times the amount of soluble 

 material found in the corresponding untreated samples. There is one 

 exception to this in the case of soil 5 at the high water content, where 

 the treated sample contained only 175 parts per million more of soluble 

 material than the untreated. It must be concluded, therefore, that the 

 increase in soluble material takes place without the evolution of increased 

 amounts of carbon dioxid and therefore is presumably due to other than 

 biological agencies. 



SUMMARY AND CONCLUSIONS 



Six different soils were treated with a saturated solution of calcium 

 sulphate. In one series of experiments the mass was transferred to filter 

 paper, permitted to drain, and then transferred to containers and the 

 rate of formation of soluble substances determined by means of the 

 freezing-point method. The treatment was found to have increased the 

 solubility of the soil to an appreciable extent. 



In another series the amount of soluble material was reduced to a 

 minimum by washing with distilled water, and the residuary effects of 

 the treatment on the solubility were likewise determined. The calcium- 

 sulphate treatment was found to have resulted in a very large increase 

 in the rate of formation of soluble substances. The effects were great 

 even when the soils were washed the second time. Obviously the treat- 

 ment results in changes in the composition of the soil mass — in other 

 words, a soil of different properties is formed. It seems that it is possible 

 to alter the composition of the soil solution and that whether such change 

 will have any effect on plant growth or not or whether the effect will be 

 favorable or unfavorable will depend upon the nature of the soil and of 

 the substances added. Moreover, it is probable that this phase of the 

 subject has not received sufficient attention in connection with our field 

 experiments. 



Two soils of somewhat different texture and organic content were 

 treated with a saturated solution of calcium sulphate, a. N/io solution of 

 calcium phosphate, and a combination of the two. The soils were 

 washed, and the rate of formation of soluble salts was determined. The 

 calcium sulphate markedly increased the solubility in each soil, while 

 the calcium phosphate decreased the rate of formation of soluble sub- 

 stances. When calcium phosphate was used in conjunction with cal- 

 cium sulphate, it counteracted the effects of the latter to some extent. 



If the carbon dioxid produced, as determined by the methods used, is 

 taken as a measurement of the biological activities, the increase in the 

 rate of formation of soluble substances brought about by the calcium- 

 sulphate treatment is due mainly to other causes. 



