32 
that precipitation or fixation from the extract may have taken place, 
since the process of extraction was extended over a period of one 
week. The results as a whole indicate the impossibility of determin- 
ing any increase in concentration of the soil solution in this type of 
soil as regards phosphoric acid by means of extraction with distilled 
water. 
The results from treatment with citric acid were somewhat differ- 
ent. Practically all pots to which phosphates were added showed a 
greater solubility in this solvent than the check pots. Furthermore, 
the solubility was more or less dependent upon the amount of phos- 
phate added to the pots. The pots showing the largest amount of 
phosphate soluble in citric acid were those to which sodium phos- 
phate had been added at the rate of 0.021 per cent, and these pots 
also produced the best growth. 
It is evident from the results obtained by extraction with fifth- 
normal nitric acid that, if this acid is a solvent for calcium phosphate, 
the lime added had little influence as regards combination with the 
phosphate, since the acid extracted little more than a trace of phos- 
phate from the soil. 
SOLUBILITY OF PHOSPHATE FERTILIZER AFTER ADDITION TO THE SOIL. 
While the preceding data indicated a variation in the solubility of 
different types of phosphate, in order to study the relation more 
thoroughly a series of experiments was planned, using the red-clay 
soil. Nineteen portions of soil of 100 grams each were weighed 
into large porcelain dishes. Duplicate portions of this soil were 
treated with each of the following phosphates, added at the rate of 
1 per cent P 2 5 : Acid phosphate, superphosphate, slag, phosphate 
rock, tripotassium phosphate, monosodium phosphate, disodium 
phosphate, commercial sodium phosphate, and monocalcium phos- 
phate. The remaining portion was used as a check. After the 
addition of the phosphate the soil was well mixed and saturated with 
water, then exposed to air and sunlight to dry and weather. Satura- 
tion and drying was repeated twice. Upon the third drying, after 
about two months' time, the different portions of soil were trans- 
ferred to percolators, and 700 cubic centimeters of distilled water was 
allowed to percolate through each sample. A separate analysis was 
made of each 100 cubic centimeters of the percolate. The results are 
given in Table IX. 
