FLORIDA STATE HORTICULTURAL SOCIETY. 
135 
mineral phosphates were stamped out, 
for even measured by a standard of pur¬ 
ity, minerals can hold their own against 
bone phosphates/’ Let us see exactly 
what acid phosphate is. The chemical 
formula of the pure tri-calcium phos¬ 
phate is Ca 3 P 208 . By recokoning atomic 
weights we find the proportion to be— 
120 lbs. calcium, 62 lbs. phosphorus, 
and 128 lbs. oxygen. Though there is 
a excess of lime, the impurities in the 
Florida rock are of no moment except 
the oxides of iron and aluminum. These 
are kept at an extremely low per cent by 
careful washing, after which the rock 
must be well dried. The process of mak¬ 
ing soluble phosphate is based on the 
stronger attraction for lime, sulphuric 
acid (H2SO4) has over phosphoric 
acid (H3PO4). The sulphuric acid 
used is very weak—only about half 
strength, for the water is needed to fa¬ 
cilitate the chemical process. While 
Voorhees ignores the fact that one 
thinks of the “parts” as being equal 
when told that a substance is divided into 
certain parts, he has made the change 
very clear to one’s mind by describing the 
rock as three parts lime to one part 
phosphoric acid. Just the right amount 
of sulphuric acid is added to combine 
with the other constituents and leave one 
part lime with the phosphoric acid, in 
which combination the phosphoric acid 
is easily dissolved. So were our acid 
phosphate pure and well made it would be 
a phosphate of lime mixed with sulphate 
of lime or gypsum. The making is mere¬ 
ly a matter of fine grinding and thorough 
mixing with the proper amount of acid. 
Things easily done in these days of first 
class machinery and skilled chemists. The 
acid, weak as it is, costs $6 per ton while 
the phosphate rock is worth less than $8, 
and it takes 63 lbs. of acid for each 100 
lbs. of pure tri-calcium phosphate. We 
can readily see that it behooves the manu¬ 
facturer to look well to the economical 
using of his acid. This same question of 
cost insures us of his being most exact¬ 
ing about impurities, for sulphuric acid 
will combine with the oxides of iron and 
aluminum before it will with the lime. 
Every 100 lbs. iron oxide will take 184 
lbs. acid and 100 lbs. alumina absorbs over 
285 lbs. of acid. The manufacturer can 
not afford impurities. Another safe¬ 
guard is the ease of detecting a poorly 
made or impure acid phosphate. If an 
excess of sulphuric acid is used it com¬ 
bines with so much lime as to leave free 
phosphoric acid. I underscore phosphor¬ 
ic, because so many think the “free acid” 
they hear about is sulphuric. The free 
phosphoric acid attracts moisture from 
the air and the fertilizer containing it is 
a damp luntpy mass. Too little sulphuric 
acid leaves some of the phosphate in the 
di-calcium, which is the same as the “re¬ 
verted” state. Too high a percentage of 
impurity makes a sticky product, high in 
insoluble phosphoric acid. We are well 
protected. It is cheaper for the manu¬ 
facturer to make a good article, and be¬ 
sides a poor acid phosphate proclaims it¬ 
self. So now we understand quite clear¬ 
ly, just what we are feeding our orange 
trees, and our next step is to learn just 
how this food reaches them and is as¬ 
similated. 
Acknowledgment due to Profs. P. H. 
Rolfs and A. W. Blair, Dr. E. R. Flint, 
Capt. R. E, Rose and others for their 
kind help over any difficult places in my 
