43 



Material. 



absorbed. Per ceut sol. in i 

 per cent citric acid. 



Sand 



Analcite 



Analcite 



Chabazite ___ 



Chabazite .__ 

 Halloysite___ 

 Halloysite ._ 

 Heulandite _. 

 Heulandite .. 



Prehnite 



Prehnite 



Pyrophyllite 



none 



o-03 5 grs. 

 0.0295 grs. 

 0.0170 grs. 

 0.0165 grs. 

 0.0125 grs. 

 0.0125 g f s. 

 0.0130 grs. 

 0.0125 grs. 

 0.0125 grs. 

 0.0120 grs. 



none 



46.5 



44.7 



100.0 



100. o 



80.8 



80.8 



loo.o 



loo. o 



77.6 



76.6 



The results show that some of the natural silicates (zeolites) 

 possess an absorbtive power for phosphoric acid, while the arti- 

 ficial preparation did so to a marked degree. The compounds 

 formed appeared to be more soluble in i per cent citric acid than 

 the compound formed when ferric hydroxide was the absorbent. 



The nature of this absorption is not understood. In the light 

 of our present knowledge of the zeolites present in the soil it was 

 considered impracticable to undertake to ascertain its nature. 



It occurred to the writer that this absorption might be due 

 to the presence of free hydrated oxide of aluminum, in which case 

 the action could not properly be referred to the silicates in ques- 

 tion. In order to determine this point, some representative sam- 

 ples of the materials used were strongly dehydrated over the 

 blast lamp and the absorptive power again determined with the 

 following results : 



Material. 



Analcite 



Analcite 



Chabazite 



Chabazite 



Precipitated silicate. 

 Precipitated silicate. 



Before dehydration 

 P2O.5 absorbed. 



0.0305 grs. 

 0.0295 grs. 

 0.0170 grs. 

 0.0165 grs. 

 o.i 340 grs. 

 o.i 340 grs. 



After dehydration. 



0.0348 grs. 

 0.0348 grs. 

 0.0170 grs. 

 0.0175 grs. 

 0.1170 grs. 

 0.1170 grs. 





With analcite dehydration seemed to increase the absorptive 

 power though only to a slight extent. Dehydration of the arti- 



