316 ILLINOIS STATE ACADEMY OF SCIENCE . 



another brown silt loam, using various phosphatic ferti- 

 lizers. As one notices from Table 1, these phosphorus- 

 carrying substances varied in their phosphorus content 

 very considerably. The amount of each substance used, 

 however, was in every case equivalent to 4 mgs. of phos- 

 phorus, as calculated from their analyses. 25 gms. of 

 soil were used in every case. Amounts of phosphorus 

 extracted with fifth normal nitric acid, as well as per- 

 cent of phosphorus recovery, are given in Table 3, and 

 are shown graphically in Figure 2. The results show 

 that, with the exception of iron phosphate and two or 

 three brands of slag, the per cent of recovery is prac- 

 tically the same. Acid phosphate gave no larger recov- 

 ery than the majority of the so-called insoluble phos- 

 phatic fertilizers. These figures are rather interesting, 

 especially if one considers them in parallel to the data 

 presented in Table 4, which has the amount and the per- 

 cent of phosphorus recovery from the same amount of 

 fertilizing material alone (without the soil), when the 

 extraction was made either with distilled water or with 

 normal fifth nitric acid. 



The data in Table 4 show that phosphorus in acid 

 phosphate is recovered with distilled water to the extent 

 of 85 per cent, and from double acid phosphate to the 

 extent of 90 per cent. None of the other phosphates had 

 solubility in water amounting to six per cent; some of 

 them, as apatite and one of the slags, were extremely 

 insoluble in water. 



When the same materials were extracted with fifth 

 normal nitric acid under the same conditions, i. e., without 

 mixing them with the soil, the per cent of recovery was 

 around 100 percent in nearly every case. See Table 4. 



It is evident that there is something in the soil that 

 prevented this phosphorus recovery. Undoubtedly some 

 of the acid, after it is added to the soil, reacts with some 

 of the soil bases, forming nitrates. This would be true 

 especially of carbonates of calcium and magnesium. 

 Such a reaction taking place would decrease the concen- 

 tration of the acid, causing a decrease in the amount 

 of phosphorus extracted. Anticipating such action in 

 some soils that are more or less supplied with carbon- 



