197 
“Soluble” phosphoric acid ‘mplies phosphoric acid or phos- 
phates that are soluble in water or in a solution of ammonium 
citrate or in a 2 per cent. solution of citric acid which approximates 
the acidity of the sap of foraging rootlets. It diffuses into the 
ground and thus reaches the feeding rootlets of the crop instead of 
lying inert in the soil, as do the mechanically mixed insoluble phos- 
phates, until the rootlets find them out and attack them. 
“Insoluble” phosphoric acid requires a stronger solvent than 
ammonium citrate to make it available as plant food. 
“Reverted, reduced, or precivitated” phosphoric acid is phos- 
phorie acid which was once soluble in water but which, by combina- 
tion with lime, iron, or aluminium in the soil, has become insoluble 
again. In that form it is, however, readily assimilated by crops. 
The chief sourcés of phosphatic manures are: 
Bones found in commerce broken up as “half-inch,” “quarter- 
inch,” and as “bonedust’”’; the finer the better, as they act more 
quickly. Commercial bones are either “raw” or “steamed” and 
degelatinised. Their respective composition is— 
Raw Bones. Steamed Bones. 
Water sis .. 10 per cent. .. 10 per cent. 
*Organic matter ... 33 ,, see AB ay 
Phosphates oe BOs we = (DS gs 
Carbonate of lime... 4 4s Sg 8-5 ,, 
Sand ses ats <2 35 a Ae ig, 
Alkaline salts es Deh s “a 4-5 ,, 
100-0 100-0 
* Equal 3-5 to 4-5 ammonia, + Equal 1-4 ammonia. 
Bone dust and half and quarter-inch have a similar composition 
to the raw product they are made from. The coarser the bones the 
heavier should the dressing be. Bonedust is applied at the rate of 
3 to 5 ewt. to the acre. 
It is often used mixed with superphosphate in equal propor- 
tions, and in the case of orchards or vineyards in full bearing ap- 
plied in quantities of 5 to 10 Ibs. per tree or 3 to 5 ewts. respec- 
tively. Where the soil is of a stiff nature and dries hard the pro- 
portion of 2 of honedust to 1 of super is preferable; whereas on 
friable loam rich in humus and fairly moist the super may pre- 
ponderate. 
Bone fertilisers are offered by the trade but are not as effective 
as bonedust, being largely a mixture of bones with other materials 
such as gypsum, marl, or superphosphate with ground rock phos- 
phate, and show a larger percentage of “insoluble” or acid soluble 
phosphoric acid. 
Ground Rock Phosphate, the raw material from which super- 
phosphate is made, contains a large quantity of phosphoric acid in 
combination with lime in the least readily available form. It is only 
useful in sour peaty soil, and being slow of action a much larger 
