for the other experiments. The results of these tests are given 

 in the following table. 



Material. ?2O5 soluble in water. 



Tri-calcium phos. 0.5 gr none 



Tri-calcium phos. 0.5 gr none 



Tri-calcium phos. 0.5 gr. am. humate 10 c.c._ none 



Tri-calcium phos. 0.5 gr. am. humate 10 c.c._ none 



Tri-calcium phos. 0.5 gr. humic acid i gr 0.0030 gr. 



Tri-calcium phos. 0.5 gr. humic acid i gr. 0.0028 gr. 



The ammonium humate was without action on the tri- 

 calcium phosphate. The free humic acid rendered a portion of 

 the phosphoric acid soluble in water, though the action was not 

 very great. These facts are in accordance with the observations 

 of other workers, namely, that humus is active in rendering 

 insoluble phosphoric acid available to plants. The results pre- 

 sented herewith indicate that this action is due to the humic 

 acid and not to the compounds of humic acid, namely, the 

 humates. 



IV. Absorption of Phosphoric Acid by Zeolites 



There is abundant evidence to show the existence in soils of 

 easily decomposable silicates analagous to the zeolites. The 

 power of these substances to fix the bases potassium, sodium, 

 calcium, ammonia, and magnesium has been thoroughly investi- 

 gated by a number of workers. 



The work of Doelter (i), Friedel (2), Rinne (3), Clarke (4), 

 and others on the constitution and properties of the zeolites, sug- 

 gested to the writer the possibility of the power of these sub- 

 stances to absorb phosphoric acid. 



For this investigation both the artificial and natural silicates 

 were used. The first was prepared by treating a solution of soda 

 alum with a solution of sodium silicate. The resulting precipi- 

 tate was washed thorougly with cold water, filtered and dried. 

 The product was difficult to wash, and seemed to undergo partial 

 decomposition even in cold water, with the elimination of sodium 

 silicate. The dry material was found to contain the following : 



