414 STATE BOARD OF AGRICULTURE 



ing and its air temperature as measured by a thermometer suspended 

 near the hydrogen electrode apparatus, rarely varied more than one de- 

 gree from 25°C during measurements. Since the temperature correc- 

 tions are small in magnitude in hydrogen ion concentration measure- 

 ments, and since errors of duplication on soils are often greater than 

 those introduced by small temperature changes, it is thought that con- 

 clusions drawn from this experimental work will not be changed by 

 introducing the temperature correction values. 



END rOINT AND Ti:srE FACTORS 



There are indications of a slight buffer action below pH 7.00 best 

 seen in curves No. 1. Also, a slightly greater rise in pH may be ob- 

 served in the vicinity of pH 7.00. Although soil acids are weak in their 

 effects and can not be expected to give distinct end points this may 

 be considered some evidence of salt formation between soil and Ca(0H)2 

 with an end point slightly above pH 7.00, indicating the possibility 

 of the formation of a salt of calcium with a weak soil acid. AVhile pH 



7.00 has been used as the point of neutralization in this work, it is be- 

 lieved that the true end point of this reaction lies slightly above pH 

 7.00. The buffering effects shown in the second group of alkali titra- 

 tion curves indicate that other end points might be obtained were the 

 titrations carried further. 



In order to test the permanence of the pH in the units lying nearest 

 jiH 7.00 readings were taken after 14 days standing and these readings 

 were close to the original ones. A quantity of Ca(0H)2 equivalent to 



3.1 cc. 0.1 N alkali was added to 30 gms. of the medium sand soil to- 

 gether with sufiflcieut water to make the total volume of liquid 50 cc. 

 and this soil required 7I/2 hours of constant stirring to bring the pH 

 down to the neutral point. In view of these and preceding results it 

 seems that at least a day's time is required to complete the reaction 

 between soil and Ca(0H)2 below pH 7.00. 



METHODS FOR DETERMINING ACTIVE BASES AND EXCESS ACIDS IN SOILS 



Methods for determining the quantity of soil bases other than iron 

 and aluminum that will react with dilute HCl, and of soil acids in acid 

 soils in excess of the quantity of soil bases were devised bnserl on the 

 foregoing experimental results. The active bases were measured by the 

 quantity of 0.2 N HCl neutralized by 20 gms. of soil; and the exvess 

 acids measured by the quantity of Ca(OH)„ required to bring the soil 

 to pH 7.00 by indirect titration, using 0.1 N equivalents of Ca(0H)2 

 and 10 gms. of soil and the hydrogen electrode as an end point indicator. 



Method For Determining Active Bases In Soils. — 20. gms. of air dry 

 soil were placed into an 8 oz. sterilizing bottle and 50 cc. of 0.2 N HCl 

 added. The bottle and contents were shaken in a machine for three 

 hours. The solution was then separated from the soil mass by filtra- 

 tion and 25 cc. drawn from the filtrate, boiled to expel COo, and titrated 

 for excess of acid with a 0.2 N KOH solution, using brom thymol blue 

 as the end point indicator, to a faint blue color. When the precipitate 

 of iron and aluminum hydroxides was voluminous it was found neces- 



