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:—

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]

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