Apr. IS, 1920 Effect of Calcium Sulphate on Solubility of Soils 51 



The results cited above immediately raise the question as to whether 

 the great increase in concentration of the soil solution resulting from 

 treatment with calcium sulphate is due to a stimulation of biological 

 activities or to chemical reactions. To throw some light on this question 

 experiments were undertaken in which the rate of production of carbon 

 dioxid was measured. The method of procedure was as follows: The 

 soils were allowed to stand over night in a saturated solution of calcium 

 sulphate. They were then filtered and washed with distilled water until 

 the concentration of the soil solution, when the soils were just saturated, 

 was only a few parts per million. The soils were then allowed to dry. 

 After thorough mixing, 60 gm. were weighed into 4-ounce bottles. The 

 desired amount of water was then added and the bottles stoppered with 

 rubber stoppers fitted with tubing so arranged that a current of air could 

 be readily drawn through the soil. The bottles were stored in the dark 

 at room temperature, and every 10 days the carbon dioxid was swept out 

 by means of a current of air free from this substance, and the amount of 

 carbon dioxid was determined. Samples of untreated soil were prepared 

 in a similar manner and the carbon dioxid determined as outlined. Tables 

 V and VI show the milligrams of carbon dioxid produced during the lo-day 

 periods and also the total production for the 30-day period at the water , 

 contents used. 



Table v.- 



-Effect of calcium sulphate on the production of carbon dioxid at high water 

 content 



Soil 

 No. 



Treatment. 



Total 



carbon 



dioxid 



produced. 



Calcium sulphate 



No treatment 



Calcium sulphate 



No treatment 



Calcium sulphate 



No treatment 



Calcium sulphate 



No treatment 



Calcium sulphate 



No treatment 



Calcium sulphate 

 No treatment 



Mgm. 

 20. 24 

 22.88 



19. 80 

 23. 10 

 23.98 

 29. 48 

 18.26 

 17.82 

 34.98 

 25.08 

 33- 88 

 34-98 



