BONE, INDUSTRIAL USES OF. There is an applica tion for every constituent of bones, the by-product of the meat trade, in various branches of industry. Besides the direct use of bones for such articles as buttons, knife-handles, etc., there is a large range of valuable secondary products. The mineral matter—phosphates, lime—is of value as artificial manure and as a component of porcelain ; the fat is worked up by the soap maker and chandler, and the gelatinous constituents are the source of much of the glue and gelatin of commerce. Further, by dry distillation, not only bone charcoal, a valuable purifying medium, but ammonia and bone-tar are obtained.
Degreasing.—For all purposes the degreasing of the bones is the first process to be carried out. The leg and thigh bones, termed "marrows" (containing 18-20% of fat), are the most valuable and are treated separately. The ends are sawn off and worked up with other bones; the marrows are steeped in weak brine for three days to free them from fibrous matter, blood, etc., and are then simmered in hot water for six hours. The boiling period is kept to a minimum lest the bones become too soft for working. The fat which rises to the surface is skimmed off. It is pale in colour and is used in pharmacy for the manufacture of pomades, and by the soap-maker. The boiled out bones are cooled, individually scrubbed to clean them, dried and sold to the button and fancy goods trade, finding their chief markets in Germany and France. The shavings and scrapings from the bone-carvers are treated for high-grade gelatin, while the fine meal from the drills, etc., finds a use in poultry- and dog-foods.
The feet of sheep, horses and cattle (the hoofs having been removed) are also treated separately by the simple boiling proc ess. These bones yield oils which are largely consumed in the manufacture of the more delicate grades of leather. Neat's foot oil (strictly the oil from the feet of cattle only), when separated from any deposited solid stearine, is used as a lubricant for deli cate machinery such as clocks, guns, etc., being valued on account of its low solidifying temperature ("cold test" 25°-28°F.).
The open boiling process only recovers about one-half of the fat contained in the bones, and is unsuitable for old and putrid bones, on account of the inferior yield and because of the offensive odour emitted from the vats. A better yield is obtained by treating the broken bones in autoclaves with open steam under two or three atmospheres pressure. If the steaming is not unduly prolonged only a small amount of the glue-yielding constituents is leached out, and a good quality fat results if fresh bones are employed. Bones contain, on an average, 12% of fat, of which 70% is recoverable by this method.
The grease may be pressed, yielding fatty bone oil which resembles neat's foot oil in its properties and is used for the same purposes.
Whale bone oil is extracted by similar treatment, but usually at the blubber-refining stations.
Benzine Process.—Practically the whole of the fat contained in bones can be recovered without any loss of gelatinous mate rial by the benzine extraction process. The fat is extracted by digesting the bones with petroleum ether (benzine) or Scotch shale oil (boiling point 212°-270°F.). The grease recovered from the extract by distilling off the solvent is dark in colour, of rank odour, and consequently unsuitable for soap-making, although on the continent a certain amount of extracted bone-fat is used for this purpose. The bulk of the product passes to the candle-maker, who recovers the fatty acids which are satisfactorily bleached by distillation.
The degreased bones are passed on to the glue makers, benzine extracted bones being very suitable. The gelatinous material is extracted by digestion with steam and hot water in open vessels, or with direct steam under pressure in autoclaves.
The weak glue liquors which are obtained as a by-product from the boiling process of degreasing can be partially concentrated, until on cooling they set to a jelly containing 75% water; this jelly is marketed as size. The glue liquors from the degelatinizing treatment are clarified if necessary with alum, and may be bleached with sulphurous acid gas ; they are then evaporated (pref erably under vacuum) to such a concentration (equivalent to about 33% dry glue) that on cooling in shallow troughs the solu tion "jellies." The jelly is cut into cakes and dried to give glue. Off-colour and twisted cakes are ground to a powder and mar keted as concentrated size. Besides its use in joinery and fur niture-making, there is a large consumption of glue in the paper and book-binding trades; the great textile industries absorb con siderable quantities of glue and size for dressing and finishing yarns, sizing woollen threads, stiffening carpets, etc. There are numerous minor applications of glue, including use in preserving ropes, in the preparation of caoutchouc substitutes, etc.
Liquid Glues.—These are glues treated with acids, such as phosphoric, acetic or nitric acid. In the presence of acid the gelatinizing property is lost and the glue solution remains liquid when cold, but the adhesiveness is unimpaired.
Gelatin.—This is prepared from bones pre-treated with hydro chloric acid to remove the phosphate of lime. Carefully picked, spongy-bones are chosen and well cleansed. The decalcified hones are treated with hot water and steam ; the fat being skimmed off, the gelatin is obtained by evaporation of the aqueous liquors. Gelatin is used for photographic emulsions, as a culture medium in bacteriology, for culinary purposes and for the clarifying of wines and beers ; it is also employed as a dressing for white fabrics, silks and straw hats.
The residual degreased and degelatinized bones are ground to a meal and used as fertilizer, being valuable on account of the phosphate of lime content. Raw bones are rarely used by the farmer. More often the bone-meals are converted into "super phosphates." To effect this the ground bone-residues are treated with sufficient sulphuric acid to convert the insoluble tri-calcium phosphate of the bones into the more soluble mono calcium phosphate which is more readily assimilated by the plants.
Dissolved Bones.—This is the term strictly applicable to the superphosphate manufactured from degreased bones only ; not being degelatinized, these bones furnish nitrogen to the soil with out the necessity for compounding with additional ammoniacal salts. The expression is loosely used for superphosphate ferti lizers made chiefly from bones.
Animal Charcoal.—One of the most valuable products from bones is animal charcoal (or boneblack) which is obtained as a residue from the carbonization of degreased bones (which may be partly degelatinized as well) out of contact with air. The bones are carbonized in retorts (usually horizontal ^ section) very similar in design to coal-gas retorts. The volatile products comprise a gas suitable for illumination and heating, a tar, and aqueous ammoniacal liquors. The tar is redistilled, giving a vola tile product condensing to "bone oil" ("Dippel's oil," "oil of hartshorn"). There is no practical use for this "bone oil," which is a mixture of pyridine and fatty amine derivatives with a most offensive odour, except as a fuel for the factory boilers. There remains in the tar-still a valuable pitch (amounting to 14 lb. per ton of bones treated) which is used in the manufacture of black varnishes such as Brunswick black. The ammonia liquors are steam-distilled and the ammonia recovered as sulphate from sulphuric acid collectors; the product is impure but suitable for fertilizer.
The residual charcoal, which is the most valuable product of the carbonization, is removed from the retorts into closed iron coolers, and protected from exposure to air until cold. It is then crushed and graded. Bone charcoal is employed as a decolourizing and refining medium, chiefly in the sugar industry, which con sumes enormous quantities; it was used in France to decolourize beet-sugar solutions as early as 1812. The fine dust charcoal is sifted out and used in the preparation of blackings and "ivory black." In sugar-refining the "char" is required from lentil to nut-size ; about one ton is needed to decolourize one ton of sugar, but the char can be revivified by washing and reburning (out of contact with air) for a life of about two years. When the decolourizing power is exhausted the spent char is discarded by the sugar manufacturer, but finds a ready market as a source of superphosphate; or it may be calcined in air to bone ash.
Bone Ash.—This, also obtained by burning fresh bones, is composed of calcium phosphate; it is used to make cupels for assaying, and is an important constituent of the paste used for "English bone china" (English soft porcelain) . When treated with sulphuric and phosphoric acids, bone ash yields a substitute for cream of tartar in baking powders.