THE VALUATION OF MANURES.
The determination of the value of a manure is in many respects a
commercial rather than a chemical question, but as it must be founded on
the analysis, and presents some peculiarities dependent on the
complicated nature of the substances to be valued, it has fallen to some
extent into the hands of the chemist. The principle on which the value
of any commercial sample is estimated is very simple. It is only
necessary to know the price of the pure article, and that of the
particular sample to be valued is obtained by making a deduction from
this price proportionate to the per centage of impurities shewn by the
analysis. Thus, for example, if pure sulphate of ammonia sells at L16
per ton, a sample containing 10 per cent of impurities ought to be
purchased for L14: 8s., and so on for any other quantity. This system
which answers perfectly with sulphate of ammonia, nitrate of soda, or
any other substance whose value depends on one individual element, is
inapplicable in the case of complex manures, such as guano and the like,
in which several factors combine to make up the value. In such cases,
manures of very different composition may have the same value, the
deficiency in one particular element being counterbalanced by the excess
of another. Hence it becomes necessary to obtain an estimate of the
value of each factor, from which that not only of one particular
substance, but of every possible mixture may be determined.
When we come to inquire minutely into this question, it appears that the
commercial value of any substance is not estimated solely by
considerations of composition, but is dependent to a great extent on
questions of demand and supply, and applicability to particular
purposes. Thus coprolites containing from 55 to 60 per cent of
phosphates 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 been
made to contrive a general system suited to all manures, and which,
though not absolutely correct, is a sufficient approximation for all
practical purposes, and a tolerably accurate guide to the determination
of their relative values.
The constituents of a manure which are of actual value are ammonia,
insoluble phosphates, biphosphate of lime (soluble phosphates), sulphate
of lime, nitric acid (as nitrate of soda), potash, soda, and organic
matter. These substances differ greatly in value. Ammonia and
phosphates, soluble and insoluble, are costly; and by far the larger
part of the value of all guanos, and the common manufactured manures,
depends on them. Nitric acid and potash are also very valuable
substances, but as they are rarely found in manufactured manures, and
never in sufficient quantity to exert any material influence in their
price, it is not usual to take them into consideration except in
particular cases. The alkali which commonly exists in artificial manures
is soda, and when alkaline salts appear in any analysis, they must be
assumed to consist almost entirely of that substance generally in the
form of common salt, and be valued accordingly. Sulphate of lime and
organic matter though abundant constituents of most manures, add but
little to their value, and it is a moot point whether they ought to be
taken into consideration, although most persons allow a small value for
them. Carbonate of lime, sand, or siliceous matter, and water, of
course, are altogether worthless.
In order to obtain the value of a manure containing several of these
substances, it is necessary to ascertain the average commercial price of
each individually. This is easily done when they are met with in
commerce separately, or at least mixed only with worthless substances,
but some of them are only found in complex mixtures, and in these cases
it is necessary to arrive at a result by an indirect process, according
to methods which will be immediately explained. The question to be
solved is the price actually paid for a ton of each substance in a pure
state, and we shall proceed to consider them in succession.
_Insoluble Phosphates._--These are purchased alone, chiefly in the form
of coprolites and bone-ash, or the spent animal charcoal of the sugar
refiners. Ground coprolites, containing about 58 per cent of phosphates,
sell at L2: 12s. per ton, which is at the rate of L4: 8s. for pure
phosphates. Bone-ash varies considerably in price, but of late samples
containing 70 per cent of phosphates have sold as low as L4: 10s. per
ton, and consequently pure phosphates in this form are worth L6: 8s. per
ton. Although these are the only forms in which phosphates are
purchased alone, it is possible to determine the price at which they are
sold in bones and phosphatic guanos, by first deducting the value of the
ammonia they contain, and assuming the remainder to represent the price
paid for the phosphates. In this way we find the following values for
insoluble phosphates:--
In Coprolites L4 10 0
Bone-ash 6 8 0
Bones 7 5 0
Phosphatic guanos 10 0 0
It is to be observed that these are actual prices, and they are liable
to fluctuate with the state of the market, although they are pretty fair
averages. It is important to notice how much they vary in the different
forms; the farmer who buys a phosphatic guano paying for phosphates a
much higher price than he could have obtained those for in other
substances--a difference which must be attributed to the high state of
division in which they exist in the guano. We do not here enter upon the
question how far this difference in price is justified; we are content
with the fact that it exists, and we are compelled to estimate the value
of phosphates in a phosphatic guano at the price given above, although
in Peruvian guano they are sold at a lower rate. For all other manures,
of which bones and bone-ash form the basis, L7 may be taken as a fair
price, and it is that usually adopted, though L8 and L10 have sometimes
been assumed as the average.
_Ammonia_ is met with in commerce as muriate and sulphate of ammonia.
The former, owing to its high price, is practically excluded from use as
a manure; the latter sells at present at from L15 to L15: 10s. per ton,
and, making allowance for the usual amount of impurity (5 or 6 per
cent), the actual ammonia is worth about L63 per ton. Calculating from
other substances it appears that ammonia is worth, per ton, in--
Sulphate of ammonia L63 0 0
Bones 61 0 0
Peruvian guano 57 0 0
the average being L60, which is the price usually adopted.
_Sulphate of Lime_ and _Alkaline Salts_ (consisting chiefly of soda) are
generally estimated at Ll per ton; and potash in those cases, in which
it is necessary to take it into account, is usually valued at from L20
to L30 per ton, the former being its value in kelp, the form in which it
can be most cheaply purchased.
_Nitrate of Soda_ is usually sold at from L15 to L15: 10s. per ton, and,
making allowance for impurities, L16 may be taken as the value of the
pure salt.
_Biphosphate of Lime, Soluble Phosphates._--Considerable difficulty is
experienced in estimating the value of these substances, because they
are not met with in commerce alone, or in any form except that of
superphosphate, and the prices at which they are sold in different
samples of that manure differ excessively. The only course by which any
result can be obtained, is to determine the average price of a good
superphosphate, and putting the values already ascertained on all the
other constituents to reckon the difference between that sum and the
market price as the value of soluble phosphates. Throwing out, as
inferior, all samples containing less than 10 per cent of soluble
phosphates, and taking the good only, I find that the average
composition of the phosphates in the market during the present year has
been--
Water 10.71
Organic matter 9.33
Biphosphate of lime equivalent to 19.43
"soluble phosphates" 12.45
Insoluble phosphates 14.78
Sulphate of lime 45.24
Alkaline salts 2.11
Sand 5.38
------
100.00
Ammonia 1.71
It is more difficult to fix the average price of superphosphate, as in
many cases no information could be obtained on this point; but among
those analyzed were samples at all prices, from L7 up to L10: 10s. per
ton, so that on the whole, L8 may be assumed as an average, and in that
case soluble phosphates are worth L27: 19s. per ton. Had the inferior
samples been included, the price would have been higher, and in fact the
rate at which soluble phosphates have been commonly estimated is L30 per
ton, or L46: 16s. for biphosphate of lime, although sometimes the former
have been reckoned as low as L25, with a corresponding rate for the
latter. It is important that biphosphate of lime and soluble phosphates
should not be confounded with one another in valuing a manure, the
latter having one and a half times the value of the former.
As manures are liable to considerable fluctuations in price, the value
attached to each of their constituents ought to be varied with the state
of the market; but it is obviously impossible for the farmer to watch
the changes in price with such minuteness as to enable him to do this,
and it is much more convenient, as well as safer, to adopt a fixed
average, which can be used with reasonable accuracy at all times. The
fact is, that this system of valuation is only an approximation to the
truth; and if absolute accuracy were aimed at, it would be necessary to
vary the estimates, not only at different times, but at different
localities at the same time, and to some extent also according to the
kind of manure. The price of soluble phosphates more especially,
fluctuates to a great extent, being practically fixed by each
manufacturer according to the facilities which his position or command
of raw material offer for producing them at a low rate. We thus find
that when made from bones alone, the cost of that substance is not
unfrequently as high as L40 per ton, and when bone-ash alone is used it
is sometimes as low as L20. Such extreme differences, of course, cannot
be taken into account in the system of valuation adopted, where all that
can be done is to take average values, which, when applied to average
samples, ought to bring out their value.
The data which have already been given regarding the price of the
individual constituents of manures can be applied to the determination
of the value of any mixture in two different ways by means of the
subjoined table:--
+----------------------------+-----------------+-------------------+
| | Price per Ton. | Per cent per Ton. |
+----------------------------+-----------------+-------------------+
| Ammonia | L60 0 0 | L0 12 0 |
| Insoluble phosphates | 7 0 0 | 0 1 5 |
| Do. in phosphatic guanos | 10 0 0 | 0 2 0 |
| Soluble phosphates | 30 0 0 | 0 6 0 |
| Biphosphate of lime | 46 16 0 | 0 9 4-1/2 |
| Alkaline salts | 1 0 0 | 0 0 2-4/10 |
| Sulphate of lime | 1 0 0 | 0 0 2-4/10 |
| Potash | 20 0 0 | 0 4 0 |
| Nitrate of soda | 16 0 0 | 0 3 2-1/2 |
| Organic matter | 0 10 0 | 0 0 1-1/4 |
+----------------------------+-----------------+-------------------+
Supposing it be desired to calculate the value of a manure by the first
column, it is obvious that if we suppose 100 tons to be purchased, the
per centages of the different constituents shewn in the analysis will
give the number of tons of each contained in 100 tons of the mixture,
and, selecting the analysis of the superphosphate given in a previous
page, we proceed in the calculation as follows:--
14.11 tons of organic matter at 10s. L7 0 0
14.86 " soluble phosphates at L30 446 0 0
15.13 " insoluble phosphates at L7 105 0 0
39.43 " sulphate of lime at L1 39 0 0
3.82 " alkaline salts at L1 4 0 0
2.10 " ammonia at L60 126 0 0
----------
Value of 100 tons L727 0 0
or L7 : 5s. per ton.
According to the second column, the numbers give the sum by which the
per centages of each ingredient must be multiplied, to give its value
in a ton of manure, and it is used for the same manure in the following
manner:--
14.11 organic matter, multiplied by 1-1/4d. L0 1 5
14.88 soluble phosphates " 6s. 4 9 2
15.13 insoluble phosphates " 1s. 5d. 1 1 4
39.43 sulphate of lime " 2-4/10d. O 8 10
3.82 alkaline salts " 2-4/10d. O O 9
2.10 ammonia " 12s. 1 5 3
--------
Value per ton L7 6 9
The difference is due to the less minute calculation of fractional
quantities in the latter case.
The calculation of the value of any other manure is effected in exactly
the same manner, taking care, however, to use the higher value for
phosphates in the case of a phosphatic guano. It will be obvious to
every one who tries the two methods that the first greatly exceeds the
second in convenience and simplicity in the calculations, and it is that
most commonly in use, although some persons prefer the second.
Although the data just given must always form the basis of the valuation
of any manure, there are a variety of other circumstances which must be
taken into account, and which give great scope for the judgment and
experience of the valuator. Of these the most important is the proper
admixture of the ingredients, and the condition of the manure as regards
dryness, complete reduction to the pulverulent state, and the like. A
certain allowance ought always to be made for careful manufacture; and,
on the other hand, where the manure is damp or ill reduced, a small
deduction (the amount of which must be decided by the experience of the
valuator) ought to be made on account of the risk which the farmer runs
of loss from unequal distribution, and the extra cost of carriage of an
unnecessary quantity of water.
It is also necessary to take into account the particular element
required by the soil. Thus, a farmer who finds his soil wants
phosphates, will look to the manure containing the largest quantity of
that substance, and possibly not requiring ammonia, will not care to
estimate at its full value any quantity of that substance which he may
be compelled to take along with the former, but will look only to the
source from which he can obtain it most cheaply. It may be well,
therefore, to point out that ammonia is most cheaply purchased in
Peruvian guano; insoluble phosphates in coprolites; and soluble
phosphates in superphosphates, made from bone-ash alone. In general,
however, it will be found most advantageous to select manures in which
the constituents are properly adjusted to one another, so that neither
ammonia, soluble nor insoluble phosphates, preponderate; but, of course,
it must frequently happen that it will prove more economical to buy the
substances separately and to make the mixture, than to take the manure
in which they are ready mixed.
In judging of the value of any manure, it is also important to make sure
that the analysis which forms the basis of the calculation is that of a
fair sample, which correctly represents the bulk actually delivered to
the purchaser, and not one which has been made to do duty for an
unlimited quantity of manure, which is supposed to be all of equal
quality, as often happens in the hands of careless manufacturers, and
too great attention cannot be devoted to the selection of the sample,
which is very often done in an exceedingly slovenly manner.