chapter I
have described the reclamation process practised by the military authorities in connection with bones arising from the cutting-up of meat for the army, as well as those recovered from the swill-tubs. As indicated, however, exploitation is conducted only to a certain point, when the bones are handed over to the degreasers. It is then that the true recovery of the commercial constituents of the bone commences. The bone is an invaluable friend to the human race as an article of commerce, though it is to be feared that what may be described as the “bone tree” is only imperfectly understood. Its far-reaching value as a fertilizer is certainly appreciated, but this really represents the final application of the article, and may be said to be the only remaining field of utility for the ultimate residue of a residue. Bones enter into a wide range of industrial and manufacturing operations. For this reason they should be carefully gathered and retained for surrender to recognized collecting mediums rather than suffer abandonment or destruction.
The housewife is prone to regard them as mere waste when she has extracted the utmost recoverable value therefrom in the kitchen. She may possibly retain them until the itinerant specialist in this commodity, to wit, the rag-and-bone man, comes round, in which event it is sure to be sped once more on a journey of industrial exploitation. But at least one-third of the bones which enter the households of Britain escape reclamation. They are wantonly wasted, and it is to be feared that the kitchen stove is mainly responsible for this loss. The volume of bones which should be forthcoming from domestic circles in Great Britain, were the dictates of thrift religiously followed, is scarcely appreciated, but it is estimated that the supply should be at least 100 tons per week from every million members of the population.
In these islands the bones are divided into two broad classes. The one division, comprising what is known as “green” (raw) bones, represents those collected from butchers’ shops, bacon-cutting works, and other similar sources. The second class, defined as “streeters,” include those forthcoming from the recognized collectors of such waste, hotels, restaurants, clubs, and private houses, and are those which have been passed through one or more cooking processes.
In the case of green bones it is customary to digest them, when really fresh, with open steam to recover the edible fat. Shank and marrow bones, as distinct from rough bones, are also able to yield a certain proportion of edible fat, and after having been digested or boiled still retain a considerable percentage of grease which it pays to extract. Consequently these, together with a certain quantity of less fresh green bones, and the streeters, are then passed through the benzine extractor to be degreased down to 1 per cent.
The shank and marrow bones are sawn up, the centre sections being selected for the production of such useful articles as knife and fork handles, buttons, and other utilitarian commodities for which their composition renders them eminently suitable. The ends or knuckles are degreased by submission to the solvent extraction process, and then, in some works, are subjected to further chemical treatment, which is somewhat elaborate, to be converted into baking-powder.
Otherwise the bones, after being degreased, are passed through other processes for the extraction of their gelatinous constituent. This is secured in the form of a liquor which is evaporated in vacuo to a jelly. The last-named is cooled into cakes and then dried on nets, or, if preferred, the liquor may be dried direct into glue-powder. By following a more complicated process gelatine can also be prepared from the degreased bones. But the gelatine thus obtained does not compare in quality with that extracted from skins. The degelatinizing process is not always followed, for the reason that some makers prefer to produce the higher quality bone-meal which is procurable from non-degelatinized bone. Obviously, however, the more profitable and economic procedure is to pass the bones through an associated glue plant.
The ultimate residue, whether degelatinised or not, is a bone-meal which constitutes the well-known fertilizer. The bone-meal, to be of the utmost feeding value to the soil, should carry little or no fat. At the same time, however, it should be rich in ammonia and phosphoric acid or superphosphate, which is determined in terms of tribasic phosphate of lime. To show how these requirements can be adequately fulfilled by submitting the raw waste to a complete recovery process, such as I have described, an analysis of a typical bone-meal produced from degreased bones--degreased by the benzine extraction process--but which have not been degelatinized, is given thus:--
Per cent. Tribasic phosphate of lime 46·60 Nitrogen, 6·07 per cent. = ammonia 7·37 Moisture 8·04 Fat 1
The high percentage of ammonia, namely 7·37 per cent., deserves especial notice inasmuch as it compares with a yield of 4·5 per cent., which is the average figure recorded with fertilizing meal obtained from steamed bones. It may possibly come as a surprise to many to learn that it is the proportion of the nitrogenous content, as represented by the ammonia, rather than the phosphoric acid content, which really determines the commercial value of this manure. The higher the figure to which the ammonia figure can be forced the more attractive the price which the fertilizer will command upon the market. Thus, under normal conditions, every 1 per cent. rise in the ammonia constituent will increase the price of the bone-meal by 14s.--$3.50. On the other hand, a 1 per cent. increase in the proportion of superphosphate only serves to increase the price of the meal by 11d. to 1s. 2d.--22 to 28 cents.
The grease obtainable from green bones varies somewhat. It is affected to a marked degree by the skill and care with which the butcher wields his knife. If the bone should be scraped very clean and carefully, naturally the bulk of the attached fat is removed. But an average collection of green bones will yield about 15 per cent., or 360 lb., of fat per ton of bones treated, while the dry bone-meal will range from 1,286 to 1,344 lb. Bones which have been collected from marine store dealers and rag-and-bone merchants are not so liberal in fat yield. The repeated cooking to which they have been subjected in connection with the preparation of dishes for the table relieves them of approximately 5 per cent. of the fat which they originally carried, i.e. in the raw condition. Consequently, degreasing only enables about 10 per cent., or 250 lb., of fat to be recovered from every ton of bones treated. In this instance the bone-meal yield may be set down at 1,568 to 1,680 lb. per ton of bones. The grease remaining in the meal varies from 0·5 to 1 per cent.
As may logically be supposed, cattle-slaughtering for food produces large quantities of blood. This is an extremely valuable residue, and so is carefully collected in suitable vessels. It is then transferred to shallow receptacles and permitted to stand for a time. Blood is composed of two fundamental constituents--the serum and the clot respectively. The former, which is the albumen, is the glutinous-like, yellowish liquid which comes to the surface, the clot settling to form as it were a sediment. The serum is recovered by skimming with a suitable device, to be distributed in extremely thin layers, applied with a brush, to dry. Such a careful procedure is imperative owing to the difficulty of drying out albumen. When dry the blood-albumen is peeled in the form of thin flakes. Its applications are numerous, one of the most important being its employment for the clarification of sugar. The clot is likewise secured to be sent to the special plant, where it is also dried.
It is common knowledge that blood constitutes a magnificent fertilizer, and this is the purpose to which the dried clot is applied. In a well-designed vacuum drying plant, such as the Scott, which has been designed especially to treat such residue, the efficiency is high. The yield from the clot may be said to range from 25 to 30 per cent.--560 to 672 lb.--per ton of raw clot treated, and is recovered in the form of a rich red dry powder.
One great objection levelled against the recovery of the blood for fertilizing purposes has been the very offensive odour which is thrown off during the drying operation. But when the task is conducted under the vacuum system no such nuisance is created, because the obnoxious gases are led to the fire to suffer combustion. In dryers of the conventional type, in which the noxious gases are removed by the aid of an exhausting fan, or suffer discharge into the chimney, the process does represent an intolerable nuisance to the neighbourhood, because there is nothing to prevent the pollution of the atmosphere. Furthermore, and this is the most important point to remember, by drying the blood under the vacuum system the ammonia content of the waste, which normally is high, can be preserved to the full, owing to the drying operation being carried out at a much lower temperature than is incidental to the usual practice.
Dried blood appeals to the farmer for the nourishment of his land essentially because of its pronounced proportion of nitrogen or ammonia. Consequently it is incumbent to keep this figure as high as possible and thus secure the advantages of market quotation. Naturally the percentage thereof in the resultant meal will vary strikingly according to the drying process practised. Ammonia is an exceedingly volatile ingredient, its tendency to escape being accentuated as the temperature employed is increased. It is only by keeping the heat factor at a low level consistent with the complete fulfilment of the desired operation, that the ammonia can be retained. Under the vacuum system this end is assured, owing to the low boiling-point due to the reduced pressure or vacuum. A typical analysis of vacuum-dried clot blood may be cited:--
Per cent. Moisture 9 Mineral matter 1·61 Nitrogen 14·02 ⤷ = ammonia 17·02
In cases where the albumen is not required separately the whole blood is dried without being separated or “clotted.”
It is obvious from what I have related, that the recovery of by-products from what has always been regarded as waste of a most repulsive character, that is from the popular point of view, can be turned to striking commercial and industrial account. Similarly it is only too apparent that such by-product reclamation as is possible demands a plant of the most complete description, to ensure all and every substance of utilitarian value being secured along the most efficient lines and to the uttermost ounce.
The day has gone when the crude methods which sufficed to satisfy individual or specific requirements should be continued. To endeavour to render it profitable to recover but one article out of many which are reclaimable simultaneously, and for the expenditure of only a little more effort, time and money, may be compared with mining for one hundred carat diamonds and allowing all those of lesser weight to fall back into the earth.
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