of the
entire farm animals in France there is no less a quantity than 76,820
tons of phosphoric acid.

As an example of how, in many cases, the amount of phosphoric acid
removed from the farm is very often much greater than that restored, a
case quoted by Crusius may be cited. This was a farm of 670 acres
(Saxon) which had received only farmyard manure, and from which, during
sixteen years, 985.67 cwt. of phosphoric acid had been sold off in the
crops; while only 408.33 cwt. had been restored in the manure, leaving a
loss of 577.34 cwt.

_Phosphoric Acid removed in Milk._

A further source of loss is the phosphoric acid removed in milk. In the
total annual yield of milk from one cow there may be from 11 to 12 lb.
of phosphoric acid.

_Loss in Treatment of Farmyard Manure._

The risks of loss of phosphoric acid in the treatment of farmyard manure
are not so great as in the case of nitrogen. There is, however, a
considerable risk, through want of proper precautions, of the soluble
phosphates being washed away by rain.

_Loss in Sewage._

The loss of phosphoric acid incurred by the present method of sewage
disposal is not so large as the loss of nitrogen, inasmuch as the
quantity of phosphoric acid contained in human excreta is very much
less. Roughly speaking, it may be said to amount to a little less than
one-third of the nitrogen lost in this way.

_Sources of Artificial Gain of Phosphoric Acid._

To balance these losses, we have a practically unlimited supply of
mineral phosphates for application as artificial manure, as well as
large quantities of other manures, many of them already mentioned in
connection with nitrogen, such as bones and guanos of all kinds. Quite
recently, also, a large source of phosphoric acid has been opened up in
the basic slag, a rich phosphatic bye-product obtained in considerable
quantity in steel-works from the basic process of steel manufacture. We
have also large quantities of phosphoric acid in the imported
feeding-stuffs, for statistics regarding which we would refer our
readers to a previous chapter. The question of the actual amount
contained in these sources is not of the same interest as in the case of
nitrogen, and need not therefore detain us. We have sufficiently
indicated the importance of phosphoric acid in agriculture by the
statements above given. All further consideration of phosphoric acid
must therefore be deferred to future chapters.

FOOTNOTES: