EXPERIMENT STATION BULLETINS. 853 



N/25 Oa(OH)2 before a change in the color of the indicator occurred, 

 using pheuolphthalein as indicator. Practically identical results were ob- 

 tained when the titration of the acid and acid salt was performed by the 

 freezing point method. 



Besides the HCl, and Al2(N03)6 other acids and acid salts were used, 

 such as HNO3, H2SO4, AICI3, Fe(N03)3, etc. The data obtained coincide 

 in principle with those above. 



Keferring now to Table 10, which contains the lime requirement of 

 soils which were treated with HCl, then washed and dried, it will be 

 observed that even this form of treatment increased the lime require- 

 ment. The increase in all soils is considerable. 



In the case of the unwashed soils to which Avere added the acid or 

 acid salts, the freezing point depression decreased with successive addi- 

 tions of Ca(0H)2 until a point was reached, the neutralization-absorption 

 point, and then it began to increase with further addition of the base. 

 The data then plotted into an acid curve similar to that obtained when 

 the acid and acid salt were titrated by the same hydrate. If there was 

 present only a very small amount of the acid or acid salt, however, this 

 acid curve could not be obtained, at least very pronouncedly, which 

 would be naturally expected. 



In the case of the soils, however, which were treated with an excess 

 of acid and then washed for long time, the freezing point depression re- 

 mained constant with successive additions of Ca(0H)2 until a certain 

 amount was added and then it began to increase. The results then 

 plotted into an absorption curve similar to that of the untreated soils. 

 The acid, or the substance which produced the acid curve, when the soils 

 were treated with an acid, was evidently removed by washing with water, 

 although an increase in the lime requirement still remained. 



The foregoing general facts finally led to the desire to ascertain whether 

 the strength of an acid changes when it is added to a soil which shows a 

 large lime requirement by the freezing point method. For obtaining in- 

 formation upon this question the following experiment was performed. 

 A soil which showed a lime requirement of about 10,000 pounds CaO 

 per acre was treated with N/100 HCl in the ratio of 10 grams of soil to 

 50 c. c. of the acid. The mixture was stirred thoroughly for a few 

 minutes and allowed to stand imtil the supernatant liquid was clear. 

 Then about 15 c. c. of this supernatant liquid was taken, without filter- 

 ing, and titrated with Ca(0H)2, according to the freezing point method. 

 To our surprise it was discovered that this supernatant liquid failed to 

 give an acid curve, and the depression began to increase almost imme- 

 diately upon adding about 2 c. c. N/25 Ca (OH) 2, indicating that the 

 liquid contained very little if any acid. Some more of the supernatant 

 liquid was taken out and tested for acidity with the litmus paper. True 

 enough the liquid was neutral or very slightly acid. It was at once sug- 

 gested that the acid or substance which gives the acid curve must be 

 in the soil mass. All the remaining supernatant liquid then was poured 

 off, the soil placed in the freezing point tube and titrated in the regular 

 manner. The results gave an acid curve as usual. These results then 

 tended to confirm the above suspicion that the acid must be in the soil 

 and very little if any of it is diff'used or represented in the solution which 

 bathes the soil. Now if that is the case, it was reasoned, the blue litmus 

 paper should turn red, when brought in intimate contact with the soil 



