EXPERIMENT STATION BULLETINS. 855 



than itself. But how and why should this soluble acid remain in the 

 soil mass and not diffuse in the supernatant liquid which bathes the soil 

 mass and thus be equally distributed? How is the law of equilibrium 

 satisfied ? 



It was thought that if the soil held this soluble acid by some means — 

 adsorption or occlusion — and did not allow it to diffuse equally into the 

 supernatant liquid — which is contrary to the law of equilibrium — then 

 there should be a difference of concentration between the supernatant 

 liquid and the sediment. This point could be easily verified simply by 

 determining the freezing point depression of the clear supernatant liquid 

 and of the sediment. The experiment was performed but the results showed 

 that there was no difference in the depression between the solution and 

 the soil — -indicating probably that the acid might not be free and in the 

 liquid phase, or if it were, it had replaced or caused something else to 

 go into solution, so that there was an equilibrium between the super- 

 natant liquid and the soil mass, as far as concentration is concerned, but 

 not in composition. 



Whatever the explanation should jwove to be, this phenomenon cer- 

 tainly appears to he a most remarkahle one. 



Having studied the effect of acids and acid salts upon the lime re- 

 quirement of soils and the phenomenon relating thereto, it will now be 

 of interest to know the results obtained with neutral salts. 



EFFECT OF SOLUBLE SALTS UPON THE LIMB REQUIREMENT OF SOILS. 



The effect of soluble salts upon the lime requirement of soils was 

 studied in two different ways: (1) to 20 grams of soil were added 20 c. c. 

 N/10 of a neutral salt solution, the soil allowed to dry in room tempera- 

 ture and its lime requirement determined according to the procedure 

 already described; (2) to 2 grams of soil were added 2 c. c. of a N/10 

 salt solution, and 10 c. c. of water, and its lime requirement ascertained 

 as usual. There were several soils used, ranging from very low to very 

 high initial lime requirement. The salt solutions employed consisted of 

 NaNOo, KNO„ CaCNOa),, KCL, ICSO,, CaCl,,, MgSO,, (NHJ„SO„ 

 NaCsHgO,, K,HPO„ and CaH^CPOJo in N/10 strength. Since both 

 methods gave essentially the same kind of results, and inasmuch as the 

 second method is the most accurate, the results obtained by the second 

 study will be presented here. These data are contained in Table 11. 



An examination of the preceding data reveals clearly and decisively 

 the following most important facts: (1) All the salts increased the lime 

 requirement of the agricultural soils very markedly, but the neutral 

 salts considerably more than the acid phosphate salts. Thus, in the 

 case of Soil No. 2 the acid phosphate salts augmented the lime requirement 

 by 1,121.8 pounds CaO per acre Avhile the neutral salts increased the 

 amount by 4,487.2 pounds; (2) All neutral salts increased the lime re- 

 quirement of any one soil to the same magnitude. This was also true 

 of the acid phosphate salts. Thus, in Soil No. 2 all the neutral salts 

 caused an increase of 4,872 pounds CaO, and both phosphate salts, 

 1,121.8 pounds CaO; (3) In the case of quartz sand which originally 

 took up no lime, none of the neutral salts caused it take up lime, but both 

 of the phosphates did. This lime requirement, however, is due to the 

 l)hosphate salts themselves and not to the quartz sand, as will subse- 

 quently be explained. 



