FLORIDA STATE HORTICULTURAL SOCIETY 
63 
phate, sometimes called bone phosphate or 
bone phosphate of lime. 
Availability and Solubility. There is 
often some confusion about the terms 
solubility and availability. Soluble phos¬ 
phoric acid means of course P. A., soluble 
in water. In addition that amount of P. 
is further considered available which is 
soluble in the neutral solution, ammonium 
citrate. So the water soluble and the cit¬ 
rate soluble together constitute the avail¬ 
able phos acid. The question of a test for 
availability will be considered later. 
The Different Compounds of Phos¬ 
phoric Acid and Calcium. These have 
many different names, but are best desig¬ 
nated by the number of atoms of calcium 
found in each compound, thus 1 part 
momocalcium phosphate, CaH6 (P2O4) 
2, a manufactured product soluble in 
water; 2 parts dicalcium phosphate, 
Ca2H4 (P 204 ) 2 , partially water soluble. 
This has taken on one more atom of Ca. 
and is said to have reverted toward the 
original substance from which it was 
made, viz: 3 parts tricalcium phosphate, 
Ca3H2 (P204)2; natural phosphate 
insoluble in water under ordinary condi¬ 
tions ; 4 parts tetracalcium phosphate—- 
partially water soluble—a problematical 
compound found in basic slag. 
The more important organic sources of 
P. as used for plant food are as follows 
(and perhaps this is a good place to state 
that organic sources as contrasted with 
the inorganic of P. do not appear to have 
the possible deleterious effects of organic 
ammonia as contrasted with inorganic) : 
1 part bone in two forms, raw and 
steamed—a possible third form is acidu¬ 
lated bone, but this has largely gone out 
of use since there is little to be gained by 
treatment with sulfuric acid, as all the 
bone becomes available sooner or later. 
Acidulated bone contains no N but 12 to 
14 per cent available P. A.; 2 parts tank¬ 
age; 3 parts phosphatic guanos. 
In comparing raw and steamed bone we 
find that raw bone has a little less P. than 
the steamed bone, but more nitrogen. It 
is not to be recommended above the other, 
however, for steaming removes the fat. 
This is not only of no use to plants, but 
reduces the availability of the tricalcium 
phosphate in the bone since it prevents 
fine grinding and forms an oily coat on the 
particles in the soil. “Other things being 
equal, the availability of any fertilizing 
element is proportional to the fineness of 
its division.’' 
2. Tankage —The composition varies 
greatly according to source—the per cent 
of tricalcium phosphate 13-39, phosphoric 
acid 2-8, the term tankage is now under¬ 
stood to include not only slaughter-house 
refuse, but even hotel refuse and general 
garbage. The nitrogen content may run 
as high as 10 per cent. The phosphoric 
acid is supposed to be about as available 
as in steamed bone. 
3. Phosphatic Guanos —These are the 
deposits of sea birds mixed with consider¬ 
able quantity of fish bones. The range of 
phosphorus content is wide, and consider¬ 
able N is present—availability about equal 
to bone tankage. All of these sources are 
rather slow and it is therefore desirable to 
use them in connection with a more quick¬ 
ly available source. All organic sources 
contain phosphorus, as tricalcium phos- 
