ates sell at about L2: 12s. per ton, while bone-ash containing the
same quantity of that ingredient brings about twice as much; in other
words, phosphates are nearly twice as valuable in bone-ash as in
coprolites, and as a phosphatic guano their price is generally still
higher; and the reason for this is obvious, in bones and guano the
phosphates are in a high state of division, in which they are easily
attacked and disintegrated by the carbonic acid of the soil, and
rendered available to plants; while in coprolites they are in a hard and
compact form, and are of little use unless they have previously
undergone an expensive preparation. In the same way, if the market price
of different kinds of guano be inquired into, very great differences are
found to exist in the rate at which phosphates are sold, and this is
attributable in part to the fact that the price at which any article is
charged commercially, is such as to cover the prime cost, expense of
freight, and other charges, and to leave a profit to the importer; and
partly, also, no doubt, to the carelessness with which manures are often
purchased, and to the want of careful field experiments in which the
effects produced by them are properly compared. It will be readily
understood that the state of division of any substance, the readiness
with which its constituents can be rendered available to the plants,
care of application, and many other circumstances must influence its
price; but making due allowance for these, differences are met with
which appear to some extent to be merely the result of caprice. It is
easy to understand why bone-ash should sell at double the price of
coprolites, but no good reason can be shewn why the phosphates in one
kind of guano should be sold at a much higher price than another, and
the difference would probably disappear if greater attention were paid
to the results of field experiments.

However great and inexplicable these differences may be, it is not the
business of the valuator of a manure to discuss them. On the contrary,
he is bound to accept them as the basis of his calculation, and to
endeavour to deduce from them a proper system of estimation for each
substance. Strictly speaking, each individual manure ought to be valued
according to a plan special to itself, and deduced from its own standard
market price; but it is obvious that this would lead to innumerable
complications and defeat its own ends, and hence an attempt has be