in the usual way. The percentages given represent 

 averages of closely agreeing duplicates for each soil 

 both ignited and unignited. 



TABLE I. PERCENTAGES 

 Soil No. 12345 



Ignited ................. 0.410 0.150 0.090 0.167 0.151 



Not ignited ............ .. 0.460 0.250 0.130 0.191 O.l'K) 



The data given in Table I leave no room for doubt 

 as to the effect of ignition on soil phosphates as ex- 

 isting in various soils. In most cases the loss in per- 

 centage is not very great, but it is always definite 

 and in some cases, as in soil No. 2, it is quite marked. 

 In practically all cases the duplicates agreed within 

 one hundredth of a percent. We obtain therefore 

 the very reverse effect of ignition on the soil phos- 

 phates as existing in the soil, from that obtained by 

 Fraps on mineral phosphates as existing in minerals. 

 In brief, ignition of soil appears to decrease appreci- 

 ably and definitely the solubility of its phosphates 

 whether they be largely inorganic or organic. The 

 large variety of soils employed would seem further 

 to strengthen the evidence, in that they doubtless 

 contained largely varying proportions of inorganic 

 and organic phosphates and a large variety of phos- 

 phate bearing minerals. 



Just why these important differences exist in the 

 effects of ignition on phosphates in minerals and in 

 soils is an explanation that is not as easily found 

 as the facts which obtain in the case. It would ap- 

 pear to be clear that the increased solubility of the 

 phosphoric acid in minerals like wavellite, variscite 

 and others tested by Fraps might be accomplished 

 through the mechanical changes induced by the heat 

 in the mineral employed. We know for example 

 that heating of sand will disintegrate its grains and 

 thus produce more surface. It is altogether likely 

 that the same happens when a phosphate mineral 

 is ignited and the result is the production of a larger 

 surface for the nitric acid to act upon, hence an in- 

 crease in solubility of phosphoric acid in the ignited 

 over the unignited mineral. On the other hand, 

 in a complex material like the soil, which contains 

 besides many kinds of mineral and rock particles in 

 different stages of disintegration, very considerable 

 quantities of organic matter, both decaying and in 

 living form, and the minerals and salts in different 

 degrees hydrated, it is probable that the mineral 

 particles would be protected from disintegration by 



(3) 



