PAPERS OX CHEMISTRY AND PHYSICS 315 



phorus extracted from the treated soil is the same under 

 these conditions as the amount of phosphorus extracted 

 from the untreated soil. 



Examination of the results in Table 2 and of the ac- 

 companying Fig. 1 reveals the rather striking fact that 

 the degree of recovery of phosphorus from nearly every 

 soil studied is practically the same, regardless of the 

 source of the phosphatic material. Water soluble double 

 acid phosphate, after it is incorporated into the soil mass 

 and moistened, becomes soluble in fifth normal nitric 

 acid, only to the same extent as the Tennessee rock phos- 

 phate. There are some relatively small differences in 

 solubility in some individual cases. On the whole, how- 

 ever, these differences are very important, as one can 

 judge from the application of Student's Method of bio- 

 metric analysis. Using -42 soil trials in which the mean 

 deviation is only -.37, and the standard deviation 3.256, 

 the ratio of the former to the latter, or Z, is only .113. 

 This value is too small to be significant. The smallest 

 value of Z used in Student's tables is .1 and such value 

 gives chances from 10 to 12 times as small as those con- 

 sidered at all significant in calculations of probability. 



Different soil types allow the recovery of different 

 amounts of phosphorus. In this respect, the variations 

 are very great. Thus, the soil of the third layer of one 

 brown silt loam (Sample 3, Table 2) did not allow any 

 recovery • while the surface layer of peat showed a com- 

 plete recovery. Indeed, the amount of phosphorus re- 

 covered from peat of the second layer was greater than 

 the amount applied. The differences are from 11 to 13 

 per cent, and seem to be larger than could be ascribed 

 to the experimental error. In the majority of cases 

 the recovery of phosphorus varied between -40 and 60 per 

 cent. On the whole, the recovery was somewhat greater 

 in the surface layer than in the subsurface. The third 

 layer, or the subsoil, gave the smallest recovery of phos- 

 phorus in all cases. 



In order to ascertain whether or not other phosphatic 

 fertilizers would follow the same general mode of be- 

 havior observed on the Tennessee rock phosphate and 

 double acid phosphate, an experiment was repeated on 



