64 
FLORIDA STATE HORTICULTURAL SOCIETY 
phate—scarcely any of it water soluble, 
blit all of it available in time, more readily 
so where favorable climatic conditions and 
the presence of lime in the soil hasten the 
decomposition of the organic matter in the 
structure of the material. 
Steamed bone is by many considered 
the preferable source of P. for citrus 
groves. The organic sources in general 
seem particularly congenial to the citrus 
family, perhaps because they contain N 
in connection with P. It is never really 
necessary to treat them with sulphuric 
acid. As further sources of P. we also 
have cotton seed meal, castor pomace, to¬ 
bacco waste, etc., all valuable and useful 
as absorbents in fertilizer mixtures, but 
more conspicuous for their N content than 
for P. 
1. The Inorganic Sources. Floats. 
This is the natural phosphate, tricalcium 
ground as fine as flour. The name was 
originally given to the dust which floated 
from the grinding mills. 
It averages - tricalcium phosphate 
associated with a slight amount of iron, 
aluminum and carbonate of calcium. 
Where soil is naturally rich in phospho¬ 
rus this is the form present. I consider 
this fact very significant. 
2. Acid Phosphate CaH 6 (^204)2. 
One hundred pounds of acid phosphate 
made from pure tricalcium phosphate 
contains forty-six pounds of monocalcium 
phosphate and fifty-four pounds of gyp¬ 
sum or land plaster—sulfate of calcium. 
If the rock phosphate contains, as it usual¬ 
ly does, also carbonate of Ca. there will 
be less soluble acid phosphate and more 
gypsum in the completed product. Acid 
phosphate may also contain some iron 
and aluminum, but raw rock which has a 
considerable content of these two minerals 
is unsuited for the manufacture of acid 
phosphate. Usually there is also present 
some undissolved tricalcium phosphate 
with which the monocalcium will react by 
taking on one more atom of Ca. and be¬ 
coming dicalcium phosphate—the reverted 
form. 
3. Dissolved Bone Black. This is 
made by treating the bone charcoal dis¬ 
carded by sugar refineries with sulfuric 
acid. The name “bone” has charms, but 
B. B. has no advantage over acid phos¬ 
phate, containing, as it does, about the same 
amount of soluble phosphoric acid. It 
may have less gypsum and less of the sol¬ 
uble Ca. may revert. There is, however, 
no superiority worth the difference in 
cost. A little lamp black mixed with acid 
phosphate will make very good bone black. 
4. Slag. Total phosphoric acid 18 
per cent. The value of slag lies in its 
phosphoric acid content and not in any 
particular name—called basic slag, slag 
meal, Thomas slag, etc. It is the finely 
ground refuse from the smelting of iron 
ores containing phosphorus—an excess of 
limestone being used in the process. The 
stone used, called dolomite, contains also 
considerable carbonate of magnesia, which 
accounts for the Mg. content of the 
• 
product. Of the P. A. only about 5 per 
cent is available, i. e., soluble in ammo¬ 
nium citrate solution. 
This brings up the whole question of 
availability. The test as provided by law 
in Florida, and nearly all other states, is 
solubility in the neutral ammonium citrate 
