BONES
_Early Use of Bones._
A most important manure, and one to the history of which very peculiar
interest attaches, is Bones. Employed first in 1774, their use has
steadily increased ever since, and their popularity as a phosphatic
manure is among farmers in this country quite unrivalled. Like guano,
although to a less extent, the early practice of using bones has done
much to arouse interest in the problems of manuring, and to bring home
to farmers the principles underlying that practice. It was from bones
that Liebig first made superphosphate of lime, and the distinguished
veteran experimenter, Sir John Bennet Lawes, has told us that the
benefit accruing from the use of bones on the turnip crop first drew his
attention to the interesting problem connected with the application of
artificial manures. Bones were first used in Yorkshire. Shortly
afterwards they were applied to exhausted pastures in Cheshire. Soon
their use became so popular that the home supply was found inadequate;
and they were imported from Germany and Northern Europe, Hull being the
port of disembarkation. So largely were they used by English farmers,
that Baron Liebig considered it necessary to raise a warning protest
against their lavish application. "England is robbing all other
countries of the condition of their fertility. Already, in her eagerness
for bones, she has turned up the battle-fields of Leipzig, of Waterloo,
and of the Crimea; already from the catacombs of Sicily she has carried
away the skeletons of many successive generations. Annually she removes
from the shores of other countries to her own the manurial equivalent of
three millions and a half of men, whom she takes from us the means of
supporting, and squanders down her sewers to the sea. Like a vampire,
she hangs upon the neck of Europe--nay, of the entire world!--and sucks
the heart-blood from nations without a thought of justice towards them,
without a shadow of lasting advantage to herself."[216]
_Different Forms in which Bones are used._
It may be pointed out that bones have done much to alter our system of
farming, by helping to develop turnip culture. Used at first in
comparatively large pieces, experience gradually showed that a finer
state of division facilitated their action. Yet it was long before the
prejudice in favour of rough bones disappeared; and it was not till 1829
that Mr Anderson of Dundee introduced machinery for preparing 1/2-inch
and 1/4-inch bones and bone-dust. In the early days of their use, bones
were fermented before being used, in order to render their action more
speedy when applied to the soil; and this practice still obtains to the
present day in some parts of the country among farmers. This
fermentation was often effected simply by mixing the bones with water,
and allowing the heap to lie for a week or two. In other cases the bones
were mixed with urine or other refuse matter. The most important step,
however, in the history of the treatment of bones for manure was the
discovery in 1840, by Liebig, of the action of sulphuric acid on them--a
discovery which led to the institution of the manufacture of
superphosphate of lime by Sir John Lawes. The nature of this action will
be explained in the following chapter, so that we need only say here
that the efficacy of the manure by treatment with sulphuric acid is more
than doubled. Bones have thus been used, and still are used, in a
variety of conditions, such as in the raw or green state, bruised,
boiled, steamed, fermented, burned, dissolved, and broken or ground into
various states of fineness, to which the names of 1/2-inch, 1/4-inch
bones, bone-meal, bone-dust, and floated bones are given. We shall now
proceed to discuss the composition of bones, and investigate more
exactly the nature of their action.
_Composition of Bones._
The composition of bone-tissue varies considerably, and depends on the
age and kind of animal to which it belongs, as well as to the part of
the animal frame from which it is taken. Bones are made up of an organic
and an inorganic part. By steeping a piece of bone in a dilute acid
solution, the inorganic portion of the bone is dissolved out, and the
organic portion, which forms the framework of the bone, is alone left.
On the other hand, by submitting a bone to the action of great heat, the
organic portion of the bone is driven off, and all that remains is a
quantity of ash. The proportion of the organic to the inorganic matter
varies considerably in different bones. The bones of young animals
contain more organic matter than those of old animals. In compact bones,
also, the organic matter is greater than in spongy bones. The
thigh-bone, of all the bones, contains most inorganic matter. In short,
bones which have to bear the greatest strain are richest in inorganic
matter. Of the bones of animals, fish-bones exhibit the greatest variety
of composition, some being almost entirely made up of organic matter,
while others are similar in their composition to the bones of
quadrupeds.
_The Organic Matter of Bones._
The organic portion of bones is almost entirely made up of a substance
to which the name _ossein_ has been given, and which, when boiled for a
long time, is converted into gelatine. This ossein, which forms on an
average from 25 to 30 per cent of the weight of bones, is extremely rich
in nitrogen, containing over 18 per cent.
_Inorganic Portion of Bones._
The inorganic portion, which forms about 70 per cent, is made up chiefly
of phosphate of lime. The dry leg-bones of oxen and sheep, according to
Heintz, have the following percentage composition:--
Per cent.
Phosphate of lime 58 to 63
Carbonate of lime 6 to 7
Phosphate of magnesia 1 to 2
Fluoride of calcium 2
Organic matter 25 to 30
According to Payen and Boussingault, raw bones contain 6-1/4 per cent of
nitrogen and 8 per cent of water. Pure bones are thus seen to contain
about 29 per cent of phosphoric acid and 6-1/4 per cent of nitrogen. The
composition of the commercial article, however, differs very widely.
This is due to the fact that bones collected from India and America,
where they have been long exposed to atmospheric influences, have lost
much of their organic matter. The amount of sand and earthy impurities
also varies very considerably.
_Treatment of Bones._
Bones are used for the manufacture of glue and gelatine. These are
extracted from them by steaming the bones. The bones after treatment are
used as a manure. The improvement noted in the action of the bones thus
treated led to the introduction of the use of steamed bones as a manure.
Raw bones are now rarely used. The fat present in raw bones retards
their decomposition in the soil. Probably, as has been suggested, it
forms along with lime an insoluble soap which prevents the mineral
matter in the bone being dissolved by the carbonic acid of the soil. In
the process of boiling or steaming a certain loss of nitrogen takes
place, greater or less, according to the length of time they are boiled
or steamed, and in the latter case the pressure applied. A more
economical method for extracting the fat has been introduced by using
benzine, but this process is not used to any extent. The loss of
nitrogen in the former case is more than compensated for by their more
speedy action as a manure when applied to the soil. Bone-meal of good
quality contains from 45 to 55[217] per cent of phosphate of lime, and
3-1/2 per cent of nitrogen. Our present total consumption of bones is
probably little less than 100,000 tons per annum, of which about half is
obtained from home collections, over 20,000 tons being annually
collected in and around London alone.
_Action of Bones._
It is well known that bones are a slow-acting manure. They may be said
to possess both a mechanical and chemical action when applied to the
soil. When they putrefy, their nitrogen is slowly converted into
ammonia, and carbonic acid as well as various organic acids are formed,
which, acting upon the insoluble mineral matter in the bones, renders it
available for plant uses. Bones thus, when applied in large quantities,
may not merely act directly as suppliers of plant-food, but in the
course of their putrefaction may act upon a certain amount of the inert
fertilising matter of the soil and render it available. The more
readily, then, bones putrefy, the more speedy will be their effect. As
we have already pointed out, bones, in order to increase their
efficiency, are often fermented before application. The removal of the
fat is another means of increasing the rate of their action, but the
fineness to which they are ground determines this more than anything
else. Much ingenuity has been expended in perfecting machinery for
grinding bones. At one time in Germany they were pounded in stamps
similar to those used for ore. In America what has been called "floated
bone" has been prepared. This bone is so fine that it actually floats in
the air like flour-dust, and is made by whirling the bones against one
another. The action of bones prepared in this way is of course very
speedy, but the difficulty of applying a manure in such a fine state of
division to the soil is great. The expense of the process also is
considerable.
The ease with which bones when ground into a fine state of division
putrefy, is evidenced by the fact that bone-flour has to be salted in
order to enable it to keep. Another condition which determines the rate
at which the fertilising matters in bones become available is the nature
of the soil. Fermentation, as we have already seen, requires a plentiful
supply of air, and a certain amount, but not too much, of moisture.
Consequently bones act best in medium soils--soils which are "neither
too light and dry, nor too close and wet." There can be no doubt that
what gives to bones a peculiar value in the eyes of the farmer is the
fact that they form a manure of a lasting character. They give what has
been termed backbone to a soil. But the tendency of modern agricultural
practice is to use quick-acting manures rather than slow. This has been
admirably put by Professor Storer in the following words: "The old
notion, that those manures are best which make themselves felt through a
long series of years, is now recognised to be an error. The adage, that
'one cannot eat the cake and have the cake' is conspicuously true in
agriculture; and just as it is the part of prudence in household or
maritime economy to abstain from laying in at any one time more
provisions than can be properly disposed of in a year or during a
voyage, so should the farmer refrain from bringing to the land an
unnecessary excess of plant-food. Such food is liable to spoil withal
in the soil, as well as other kinds of provisions that are kept too long
in store. A just proportion of food, properly prepared, is the point to
be aimed at always."
In view, therefore, of what has just been said, it might seem best to
use bones in the form in which they are most speedily available--viz.,
as dissolved bones. This would be so if bones were the only source we
possessed for the manufacture of superphosphate of lime; but we now
have, in the various mineral phosphates, abundant and cheaper sources of
this valuable manure. The opinion of leading agriculturists and
agricultural chemists is rather in favour of applying bones in the
undissolved condition. For one thing, it seems far from economical to
utilise an expensive material such as bones for manufacturing an article
which can be equally well manufactured from cheaper materials; for once
the phosphate of lime is dissolved, it is equally valuable from whatever
source it may be derived. Of course this is not tantamount to saying
that dissolved bones as a manure are no more valuable than
superphosphate. In dissolved bones we have, in addition to soluble
phosphate, a considerable proportion of undissolved bone-tissue,
containing a certain quantity of nitrogen and organic matter; but so far
as the soluble phosphate is concerned, it seems only rational to
conclude that its efficacy is equally great, whether it be derived from
bone or mineral phosphate. Another reason is, that much of the
characteristic action of bones is lost by treating them with sulphuric
acid. As Dr Aitken has pointed out, the germ life in the soil and in the
bones gradually converts them into a form available for the nourishment
of plants; but to dissolve bones with sulphuric acid is to kill out the
germ life and retard the decay of any nucleus of bone in the dissolved
manure.
_Dissolved Bones._
Dissolved bones, however, are still manufactured. Formerly the manure
called dissolved bones was often a mixture of mineral superphosphate
along with undissolved bone-meal, but recent legislation has stopped the
continuance of this practice. The composition of dissolved bones varies
somewhat, the percentage of soluble phosphate being about 20 to 23 per
cent, the insoluble amounting to from 9 to 10 per cent, and the nitrogen
from 2-1/2 to 3-1/2 per cent.[218] Another reason against dissolving
bones is to be found in the difficulty experienced in dissolving their
phosphate. Bones, especially when raw, are not easily acted upon by
acids.
_Crops suited for Bones._
Bones are commonly regarded as being specially beneficial to
pasture-land, to which they are applied as a top-dressing. Turnips,
tobacco, potatoes, vines, and hops are also much benefited by the
application of bones. In America, mixed with wood-ashes (the chief
manurial constituent of which is potash), they have been extensively
used as a substitute for farmyard manure, and have been applied at the
rate of 5 to 6 cwt. per acre. In Saxony, according to Professor Storer,
1 cwt. of fine bone-meal is worth as much as 25 to 30 cwt. of farmyard
manure.
_Bone-ash._
The ash which is left on burning bones used to be an article of
considerable manurial importance. It is still imported from South
America in some quantity, and is used chiefly in the pottery industry.
It is occasionally still used to a limited extent for the manufacture of
high-class superphosphates. It is extremely rich in phosphate of lime,
of which it contains between 70 and 80 per cent; but of course it is
devoid of nitrogen.[219] Bone-ash is best used in the dissolved form, as
it possesses no characteristic action such as is possessed by bones.
_Bone-char or Bone-black._
When heated in a closed retort, bones are not converted into bone-ash,
but into a body called bone-char. This body is similar in composition to
bone-ash, except for a certain percentage of charcoal--amounting, on an
average, to 10 per cent. It contains but little nitrogen and other
organic matter. Bone-black or bone-char is an article which is prepared
in enormous quantities for use in sugar-refineries, where it is used in
the purification of sugar. After use it may be renovated by submitting
it to heat; but as this process gradually lessens the percentage of
carbon it contains, after a certain period it becomes too poor in this
substance for efficiently acting as a filter. When this takes place it
is technically known as spent char, and is used for the manufacture of
superphosphates. Spent char is a highly phosphatic substance, being very
little poorer than bone-ash, and containing about 70 per cent of
phosphate of lime.[220]
FOOTNOTES:
[216] It is only fair to Liebig to say that when he wrote these words
the practically boundless supply of mineral phosphates which we now know
to exist in many parts of the world was little dreamt of.
[217] See Appendix, Note I., p. 371.
[218] See Appendix, Note II., p. 371.
[219] See Appendix, Note III., p. 372.
[220] See Appendix, Note IV., p. 372.
APPENDIX TO CHAPTER XI.
NOTE I. (p. 364).
The following analysis will serve to show the composition of
bone-meal:--
Moisture 10.43
*Organic matter 32.30
Phosphate of lime 48.40
Carbonate of lime, magnesia, &c. 7.20
Insoluble siliceous matter 1.67
------
100.00
------
*Containing:--
Nitrogen 3.71
Equal to ammonia 4.51
NOTE II. (p. 368).
COMPOSITION OF DISSOLVED BONES.
The accompanying analysis may be taken as representing the average
composition of dissolved bones:--
Moisture 10.10
*Organic matter and water of combination 29.34
Monobasic phosphate of lime 11.23
(Equal to tricalcic phosphate rendered "soluble" 17.58)
Phosphate soluble in ammonium citrate 14.02
Insoluble phosphate of lime 1.88
Calcium sulphate, magnesia, alkalies, &c. 30.23
Sand 3.20
------
100.00
------
*Containing:--
Nitrogen 2.62
Equal to ammonia 3.18
COMPOSITION OF COMPOUND BONES.
The following analysis illustrates the composition of compound bones:--
Moisture 8.10
*Organic matter and water of combination 37.22
Monobasic phosphate of lime 13.68
(Equal to tricalcic phosphate rendered "soluble" 21.42)
Insoluble phosphate of lime 10.48
Calcium sulphate, magnesia, alkalies, &c. 26.02
Sand 4.50
------
100.00
------
*Containing:--
Nitrogen 1.90
Equal to ammonia 2.30
NOTE III. (p. 369).
As showing the composition of bone-ash, the following analysis may be
quoted:--
Moisture .25
Organic matter .85
*Phosphoric acid 35.56
Lime 47.09
Magnesia, alkalies, &c. 9.80
Sand 6.45
------
100.00
------
*Equal to tricalcic phosphate 77.63
NOTE IV. (p. 370).
Composition of bone-char (on dry sample):--
Carbon 10.51
Calcium and magnesium phosphates, calcium fluoride, &c. 80.21
Calcium carbonate 8.30
Calcium sulphate .17
Ferric oxide .12
Silica .34
Alkaline salts .35
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100.00
------