h; or by drainage of the soluble nitrogen compounds, caused by
allowing the rich black liquor of the manure-heap to be washed away, and
not properly conserved.

_Nitrogen removed in Milk._

Another source of loss which is apt to be overlooked is the amount of
nitrogen removed in milk. Professor Storer has calculated that in the
case of a cow giving 2000 quarts, or 4300 lb., of milk in a year, and
the milk being all sold as such, there would be carried away from the
farm 22 lb. of nitrogen.[89]

_Economics of the Nitrogen question._

And here, before concluding our survey of the different sources of loss
of nitrogen, it may be well to regard for a moment the subject from a
somewhat wider standpoint than that from which we have been considering
it. The total supply of nitrogen in a combined form is limited. As we
have pointed out, it may be regarded as the element on which, more than
any other, life, animal as well as vegetable, depends. To animal life it
is alone available in combined form; to vegetable life it is chiefly
also only available in combined form. In the air we have an unlimited
quantity of nitrogen, but it is almost entirely in an _uncombined_ form,
and therefore largely unavailable. The conversion of nitrogen from the
free state to a combined form is a process which takes place only very
slowly. Any source which diminishes the sum-total of our already all too
limited supply of combined nitrogen must be regarded as worthy of most
serious consideration. The question, therefore, of the artificial waste
of nitrogen daily taking place around us, is one which ought to possess
for economists a very great interest indeed. This waste has, of late
years, enormously increased, and would seem to threaten us at no very
distant date with a nitrogen famine. It is incidental to the use of
certain nitrogenous substances in the manufacture of various articles,
and to our present system of sewage disposal.

_Loss of Nitrogen-compounds in the Arts._

The articles referred to are such as explosives, starch, textile
substances, malt liquors, &c. The question is strikingly dealt with in
an able paper on "The Economy of Nitrogen" in the 'Quarterly Journal of
Science.'[90]

_Loss due to Use of Gunpowder._

The explosives--more particularly gunpowder--are the most important of
these articles. Gunpowder contains 75 per cent of saltpetre, which in
its turn contains about 10 per cent of nitrogen. When gunpowder
explod