large amount of experimental work that has been done
affords data that causes the following opinion to be stated here:
Rock-phosphate, known as floats, is not a profitable source of
plant-food for soils deficient in organic matter, when compared with
acid phosphate. It is more nearly profitable in an acid soil than in
one that has no lime deficiency. It gives more satisfactory results
when mixed intimately with stable manure than when used upon land that
remains deficient in organic matter. Applications should be in large
amount per acre--500 to 1000 pounds--in order that the amount of
readily available phosphoric acid may meet the immediate need of
plants. Dependence should be placed upon the readily available acid
phosphate in all instances until experiment on the farm shows that the
rock-phosphate is a cheaper source of plant-food than the acid
phosphate.

Acid Phosphate.--When animal bone is treated with sulphuric acid, the
result is an acid phosphate, but treated animal bone is so rare on the
market that it may be ignored. The acid phosphate on the market is
rock-phosphate treated with sulphuric acid to render its plant-food
available. The content of phosphoric acid varies because the original
rock-phosphate varies, but the most common grade on the market is
guaranteed to contain 14 per cent available phosphoric acid, and 1 to 2
per cent insoluble. Some acid phosphate is guaranteed to contain 16 per
cent available phosphoric acid, and some runs down to 10 per cent
available.

An acid phosphate contains quickly available plant-food. A prejudice
exists against it on account of its source, and it has been a common
practice to label the bags "bone-phosphate," or "dissolved bone," or
such other designation as would imply an organic source, but the acid
phosphate is made out of rock-phosphate, regardless of the name given.
The prejudice against the rock as a source of plant-food is giving way.
It is our chief and cheapest source of supply. The combination of
sulphuric acid with rock-phosphate in the production of acid phosphate
produces sulphate of lime, known as gypsum or land-plaster. The amount
of gypsum in a ton of acid phosphate varies, but may be roughly
estimated by the buyer as two thirds of the total weight of the acid
phosphate.

The tendency of gypsum is, in the long run, to make a soil acid, and
its use necessarily hastens rather than retards the day when a lime
deficiency will occur. The influence in th