ELLS HA MITCHELL SCIENTIFIC SOCIETY. 



123 



tent of sesquioxides of iron and alumina (the iron here is really 

 present as the protoxide) is only 1.795 per cent., the total pre- 

 cipitation during the whole period of 27 weeks is the slightest ; that 

 is, only 4.05 percent, soluble phosphoric acid (in this case, how- 

 ever, other ingredients exert their influences, as will be discussed 

 later), corresponding to 31.69 per cent, of the total soluble phos- 

 phoric acid present. In soil 1, containing the next highest con- 

 tent of iron and alumina (3.845 percent.), the total precipitation 

 is 7.55 per cent, soluble phosphoric acid, corresponding to 59.30 

 per cent, of the total soluble phosphoric acid. In soil 4, with 

 the third higher content of iron and alumina (8.275 per cent.), 

 the precipitation is 8.89 percent., or 69.90 per cent, of the whole 

 soluble phosphoric acid originally present. And lastly, in the 

 soil containing the largest amount of iron and alumina (28.125 

 per cent.) the precipitation amounts to 11.17 per cent, for the 

 whole period, corresponding to as much as 87.81 percent, of the 

 whole soluble phosphoric acid originally present. By referring 

 to Table VIII this change can more readilv be seen. 



TABLE VIII. 



SHOWING TOTAL PRECIPITATION OF SOLUBLE PHOSPHORIC ACID DURING 



27 WEEKS WITH VARIOUS Soil.-. 



As was referred to above in the case of soil 3, the precipitation 

 is slight, due no doubt, 1st, to the small amount of iron and 

 alumina present, but principally to the large content of organic 

 matter present in the soil. The presence here of the organic 

 matter, and the formation of organic acid, retards the decompo- 

 sition of the soluble phosphate and consequently the change to 

 the precipitated form. 



Let us now look at the effect of the soils on the acid phosphate 

 in regard to the insoluble phosphoric acid. With soils 1 and 4 

 there has been no change in the insoluble from the beginning to 

 the end of the period; or if any exists it is slight and within the 



