Aug. 1, 1925 
Colloidal Silica and Efficiency of Phosphates 
255 
quantities of P 2 0 5 and Si0 2 found in solution, 3 calculated for the 
250 cubic centimeters of solution, are shown in Table III, together 
with the special treatments of each flask. 
Table III .—Soluble phosphoric acid obtained from rock phosphate and acid phos¬ 
phate in a mixed salt solution with or without silica gel 
Contents of flasks (in addition to 1.25 grams mixed salts and 250 cubic centimeters 
water) 
Phos¬ 
phoric 
acid 
(P 2 O 5 ) 
in solu¬ 
tion in 
250 cubic 
centi¬ 
meters 
Silica 
(SiOt) 
in solu¬ 
tion in 
250 cubic 
centi¬ 
meters 
0 5 gram rnelr phnsphat.fi __ _ 
Gram 
0.0010 
Gram 
0.0021 
0 5 gram rock phosphate, 5 grams silica gel.... . _ - 
.0012 
.0184 
0 5 gram roek phosphate, 15 grams silica gel ____ _ ___ 
.0019 
.0207 
0 5 gram rook phosphate, 30 grams silica gel __ _ __ 
.0045 
.0229 
0,3 gram acid phosphate _ _ __ __ 
.0344 
.0025 
0 3 gram aoiri phosphate, 15 grams silica gel __ _____ 
.0346 
.0231 
The 30-gram addition of silica gel appears to have markedly in¬ 
creased the quantity of phosphoric acid brought into solution from 
rock phosphate. 4 The increase produced by 15 grams of gel also 
appears real, but that attributable to the 5 grams of gel is probably 
less than experimental error. The solubility of the acid phosphate 
P 2 0 5 in the salt solution was apparently not affected by the silica gel. 
In order to check the accuracy of these results, a second test, 
similar to the first, was conducted with the rock phosphate. The 
method and materials of the second test were the same as those of 
the first, but the quantities of phosphate, gel, and salts were some¬ 
what different; also most of the different treatments were duplicated. 
One flask (the last in the table) was included in which the mixed 
salts were varied solely by omitting the iron. The mixtures were 
allowed to stand 12 days with an occasional shaking. The results 
of this second test are given in Table IV. 
Table IV .—Soluble phosphoric acid obtained from rock phosphate in a mixed salt 
solution with or without silica gel 
Contents of flasks (in addition to 1.64 grams of mixed salts and 
251 cubic centimeters water) 
Phosphoric acid: 
(P 2 O 5 ) in solu¬ 
tion in 251 cubic 
centimeters 
Silica(Si O 2 ) in solu¬ 
tion in 251 cubic 
centimeters 
Individ¬ 
ual 
flasks 
Average 
of dupli¬ 
cates 
Individ¬ 
ual 
flasks 
Average 
of dupli¬ 
cates 
No phosphate, 31.3 grams silica gel-1- 
Rock phosphate containing 0.15 gram P 2 O 5 - 
Rock phosphate containing 0.15 gram P 2 O 5 ,31.3 grams silica gel.. 
Rock phosphate containing 0.15 grams P2(>8,31.3 grams silica gel, 
no Fe in mixed salts _ _ 
Gram 
( 0.0011 
\ .0006 
j .0006 
\ .0005 
/ .0054 
\ .0054 
.0067 
Gram 
} 0.0009 
} .0006 
j- .0054 
Gram 
j 0.0228 
\ .0187 
/ .0023 
\ .0021 
/ .0237 
\ .0227 
.0215 
Gram 
} 0.0208 
} .0022 
} .0232 
s The quantity of silica shown as “in solution’' represents the quantity passing through the Pasteur - 
Chamberland filter. Part or all of this may have been present as a very finely dispersed sol rather than as 
a true solution. v . . . x . . . , 
4 Similar results were obtained by Mattson (U, p. 77) on digesting a precipitated tncalcium phosphate 
with water suspensions of sphagnum peat, ceramic clay and quartz flour. The first two substances were 
particularly effective in decomposing the phosphate. 
