126 JOURNAL OF THE 



Here we see that the increase of the amount of soil increases 

 the total precipitation, and increases also the amount of phos- 

 phoric acid rendered insoluble by the formation of basic phos- 

 phate of iron and alumina. The results are as would be ex- 

 pected in regard to the increase, but as to the amount of the 

 increase the results are somewhat surprising. 



For here, when the quantity of soil is three times what it 

 was in the first experiment, the precipitation is only 0.14 per 

 cent, greater in phosphoric acid; and with 6 times as much soil 

 the total precipitation is only 0.30 per cent. And again, where the 

 soil is four times greater, the insoluble phosphoric acid remains 

 practically the same; and with six times as much soil gives an 

 increase of only 0.18 per cent, phosphoric acid. Results like 

 these, where would be expected a greater increase, seem to be 

 anomalous. 



Probably the only rational explanation which can be given is 

 the following : When the superphosphate comes into intimate con- 

 tact with the soil the particles of the former are surrounded by 

 larger masses of the latter. Each separate particle of the phos- 

 phate, therefore, must be mingled with numerous particles of 

 the soil, so that the soil particles touch it at all possible points, 

 The number of the soil particles is of course limited by their 

 fineness, and it can be easily seen that the number can be fixed; 

 or, iu other words, that a given particle of acid phosphate can 

 only come in contact with a limited number of given soil par- 

 ticles. With this view, the anomaly can be explained by con- 

 sidering that the phosphate particle in the mixture is surrounded 

 by a definite number of soil particles, and that this number is 

 nearly reached when the mixture is 1: 32. A large increase 

 of soil, therefore, has but little effect on the subsequent precipi- 

 tation, for the additional soil particles cannot touch the already 

 surrounded particle of the phosphate. 



If this theory be correct, then, the series of experiments 

 (Table IX) do not fall far short of what would actually be the 

 case when the superphosphate is applied to the soil, if the latter 

 remains in a continuous moist condition, and if the effect of 

 heavy rains be disregarded. 



