Mar. i, 1921 Relation of Calcium Content to Soil Reaction 



859 



minutes, the soil suspension was considered to be at equilibrium. This 

 point was noted and taken as the initial reaction of the soil. A solution 

 of saturated calcium hydroxid is very near N/24. For the sake of facility 

 in making calculations this was made iV/25. Since the final end product 

 of calcium hydroxid or calcium oxid added to the soil is calcium carbonate, 

 this equivalent is used in making the calculations. One cc. of NJ25 cal- 

 cium hydroxid is equivalent to 0.002 gm. of calcium carbonate. One 

 acre of soil 7 inches deep is assumed to weigh 2,000,000 pounds. Since 10 

 gm. of soil were used in a determination, the ratio of the calcium car- 

 bonate equivalent of 1 cc. of the calcium hydroxid is 1 : 5,000. Accordingly, 

 each cubic centimeter of calcium hydroxid used to titrate is equivalent 

 to 400 pounds of calcium carbonate per acre. 



When the voltmeter reading at the initial equilibrium point had been 

 obtained, the calcium hydroxid was added from the burette in small por- 

 tions at a time until the equilibrium was again obtained at voltmeter 

 reading equivalent to P H 7. The total number of cubic centimeters used 

 in the titration were recorded, and again small portions of calcium hy- 

 droxid were added till equilibrium was established at voltmeter reading 

 equivalent to P H 8.3. This is approximately the titration end point for 

 phenolphthalein. Again the calcium hydroxid was added until equili- 

 brium was established at reading equivalent to P H 10. The latter point 

 was somewhat arbitrarily chosen. 



A few grams of special " K " calcium carbonate were suspended in water, 

 and after long shaking the reaction was found to be P H 9.23. This is a 

 little lower alkalinity than the value P H 9.5 obtained by Sharp and Hoag- 

 land (10). The reading P H 10 denotes a higher alkalinity than that 

 found in a normal soil. 



The electrometric measurements then gave these data: The initial re- 

 action of the soil suspension stated as P H ; the total number of cubic cen- 

 temeters of calcium hydroxid (Af/25) required to change the reaction 

 to P H 7, P H 8.3, and P H 10, respectively. The results of these measure- 

 ments are recorded in Table II. 



Table II. — Initial reaction of the soil and tlie number of cubic centimeters of NJ25 calcium 

 hydroxid used to change the reaction to the figures given ° 



GROUP I. SOILS WHOSE INITIAL REACTION WAS MORE ALKALINE THAN IS INDICATED BV Ph 8.3 



Soil 

 No. 



1 169 

 1227 

 1043 

 1221 

 I2Q7 

 1 199 

 III9 

 I206 

 1 186 



County. 



Reno 



Greenwood 

 Russell . . 

 Greenwood 

 Montgomery 



Jewell 



Finney. . 

 Jewell. . . 

 Reno. . . . 



Soil type. 



Pratt loamy fine sand 



Crawford clay 



Benton loam 



Oswego silt loam 



do 



Laurel very fine sandy loam . 



Dune sand 



Lincoln silty clay loam 



Kirkland clay loam 



Initial 

 Ph. 



8.61 

 8.56 

 8.52 

 8.51 

 8.46 

 8.44 

 8.44 

 8.40 

 8-37 



Cubic centimeter^ of Ca(OH)s 

 required to titrate to — 



Ph 7. 



Ph8. 3 . 



0.7 

 5-4 

 3-7 

 9-3 

 2-5 

 12.3 

 4.4 

 4.0 



° Figures arranged according to increasing hydrogen-ion concentrations. 



