42 



Alumina 18. 12% 



Silica 57-21% 



Soda 5.! 



Water .. i8.i 



Two grams of this substance were treated with superphos- 

 phate solution, allowed to stand seven days, filtered, washed, and 

 the phosphoric acid in solution then determined. The residues 

 were treated with 100 c.c. of i per cent citric acid solution and 

 allowed to stand for twenty-four hours. The phosphoric acid 

 dissolved by this reagent was then determined, with following 

 results : 



No. P2O 5 absorbed. Per cent sol. in i 



per cent citric acid, 



1 O.I340grs. 56.8 



2 o.i34ogrs. 57.4 



The natural silicates used were selected with a view of ob- 

 taining as much variety in composition as possible. A few insol- 

 uble silicates were also used. 



It is not within the province of this paper to enter into a 

 discussion of the constitution of these compounds. The empir- 

 ical formulas are given herewith. 



Analcite _. NaAlSi 2 O 6 H 2 O 



Chabazite (CaNa 2 )Al 2 Si 4 O 12 6H 2 O 



Halloysite H 4 Al 2 Si 2 O 9 aq. 



Heulandite H 4 CaAl 2 (SiO 3 )6 3H 2 O 



Prehnite H 2 Ca 2 Al 2 (SiO 4 ) 3 



Pyrophyllite H 2 Al 2 (SiO 3 ) 4 



In order to determine the absorptive power of these sub- 

 stances for phosphoric acid, 2 gram portions of each were placed 

 in small flasks, and to each were added 50 c.c. of a solution of 

 superphosphate containing o. 1550 gram P 2 O 5 . The experiment 

 was carried out in the manner described for the precipitated sil- 

 icate. Solubility determinations of the residues, in i per cent 

 citric acid were made in a similar way. A check determination 

 was made with washed sand. The following table contains the 

 data obtained. 



