Soluble and Insoluble Phosphates. 
159 
mineral phospliates — such as Norwegian, Canadian, 
and Spanish apatite — arc less soluble than in the shape 
of porous phosphatic materials, such as certain kinds 
of jihosphatic guano and semi-fossilized rock-guano, 
for the simple reason that the particles of phosphate of 
lime are more finely divided, and in every case more 
soluble in water in the more porous materials than 
in crystalline hard materials. 
G. I3y treatment with acid the phosphate of lime in phos- 
phatic materials is rendered perfectly soluble in water, 
and on the application of dissolved phosphatic mate- 
rials (superphosphate) to the soil, the soluble phosphate 
contained in the superphosphate is precipitated and 
rendered insoluble by contact with the soil. 
7. In this precipitated condition insoluble phosphate of 
lime is infinitely more finely divided, and in conse- 
quence greatly more efficacious, than in the finest state 
in which the raw materials used by makers of super- 
phosphate can be obtained by mechanical means. 
8. In my judgment, chemical treatment with acid is the 
most economical and best plan of utilising mineral 
phosphates for agricultural purposes. 
To persons wishing to institute practical experiments relating 
to this matter, I would recommend the following scheme in 
duplicate experiments : — 
General Scheme of Swede Trials, One-fourth of an Acre. 
1. 4 cwts. dissolved coprolites (contaiuing 25 per cent, sohible phos- 
phates), costing about 1?. per acre. 
2. 6 cwts. raw coprolites finely powdered, at a cost of about 1^. per acre. 
3. cwts. fine bone-meal „ „ 
4. 3 cwts. dissolved bone-meal .... „ „ 
5. 3 cwts. precipitated phosphate of lime „ „ 
6. Nothing. 
7. 6 cwts. of Redonda phosphate finely ground) 
(anativephosphateof alumina andiron)) " " ' 
8. Rotten dimg, 20 tons „ „ 
9. Rotten dung, 10 tons, and 4 cwts. dis-) 
solved coprolites J " " 
10. Rotten dung, 10 tons, and 6 cwts. of coprolite powder, per acre. 
11. Chalk, at the rate of 5 tons per acre. 
Each experimental plot should not be less than l-4th of an acre. 
Swedes to be the experimental crop ; on one plot 4 cwt. per acre 
of superphosphate, containing 25 per cent, of soluble phosphate 
(dissolved coprolites), costing about 1/. per acre, is to be applied, 
and to the other manured plots various phosphatic fertilisers, 
likewise at a cost of about 11. per acre in every case. 
