HORN, in physiology, a hard substance growing on the heads of divers animals, particularly the cloven-footed quadrupeds; and serving them both as weapons of offence and defence.
The horn of animals is of the same nature as their gelatinous matter; and is only that matter charged with a less quantity of water, and a larger quantity of earth, and sufficiently condensed to have a firm and solid consistency. By digesting horn with water in Papin's digester, it may be entirely converted into jelly.
Horn is a perfectly animalised matter, and furnishes in distillation the same principles as all animal-matters; that is, at first a pure phlegm, with a degree of heat not exceeding that of boiling water; then a volatile alkaline spirit, which becomes more and more penetrating and strong; a fetid, light, and thin oil; a concrete volatile salt, which forms ramifications upon the sides of the receiver; much air; fetid oil, which becomes more and more black and thick; and lastly, it leaves in the retort a considerable quantity of almost incombustible coal, from which, after its incineration, scarcely any fixed alkali can be obtained.
Animal oil, and particularly that which is drawn first in the distillation of horn, is susceptible of acquiring great thinness and volatility by repeated distillations, and is then called the oil of dippel.
The horns of flags, and of other animals of that
kind, are the most proper to furnish the animal oil to be rectified in the manner of dippel; because they yield the largest quantity. These horns also differ from the horns of other animals in this, that they contain a larger quantity of the same kind of earth which is in bones; hence they seem to possess an intermediate nature betwixt horns and bones.
Hart's Horn. See HART'S-HORN.
Hart's-Horn calcined to Whiteness. The phlogiston of the coal of hart's-horn, although very difficultly combustible, may nevertheless be burnt with more ease than the coal of other horns, and with nearly the same facility as bones may. This coal, by being calcined with a long-continued and strong fire, is changed into a very white earth called hart's-horn calcined to whiteness. This earth is employed in medicine as an absorbent. It is given in dysenteries and labour-pains which are supposed to be caused by acrid and ill-digested matters. Hart's-horn calcined to whiteness and levigated, is the basis of Sydenham's white decoction, which is commonly prescribed in these diseases.
Hart's-Horn prepared philosophically. This name is given to hart's-horn deprived by water of almost all its gelatinous part, so that its becomes brittle; and when its outer part is taken off, it is thus rendered very white, and is applicable to the same uses as that which is calcined by fire.
Dyeing of Horn—Black is performed by steeping brafs in aqua-fortis till it be returned green: with this the horn is to be washed once or twice, and then put into a warmed decoction of logwood and water. Green is begun by boiling it, &c. in alum-water; then with verdigris, ammoniac, and white-wine vinegar; keeping it hot therein till sufficiently green. Red is begun by boiling it in alum-water, and finished by decoction in a liquor compounded of quick-lime steeped in rain-water, strained, and to every pint an ounce of Brazil-wood added. In this decoction the bone, &c. is to be boiled till sufficiently red.
Dr Lewis informs us that horns receive a deep black stain from solution of silver. It ought to be diluted to such a degree as not sensibly to corrode the subject; and applied two or three times, if necessary, at considerable intervals, the matter being exposed as much as possible to the sun, to hasten the appearance and deepening of the colour.
Dyeing or staining Horn to imitate Tortoise-shell.—The horn to be dyed must be first pressed into proper plates, scales, or other flat form; and the following mixture prepared. Take of quick-lime two parts, and of litharge one part; temper them together to the consistency of a soft paste with soap-ley. Put this paste over all the parts of the horn, except such as are proper to be left transparent, in order to give it a nearer resemblance of the tortoise-shell. The horn must remain in this manner covered with the paste till it be thoroughly dry; when, the paste being brushed off, the horn will be found partly opaque and partly transparent, in the manner of tortoise-shell; and when put over a foil, of the kind of latten called assidue, will be scarcely distinguishable from it. It requires some degree of fancy and judgment to dispose of the paste in such a manner as to form a variety of transparent parts, of different magnitudes and figures, to look like the effect of nature: and it will be an improvement to add
femi-transparent parts; which may be done by mixing whitening with some of the paste to weaken its operation in particular places; by which spots of a reddish brown will be produced, which if properly interspersed, especially on the edges of the dark parts, will greatly increase both the beauty of the work, and its similitude with the real tortoise-shell.