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sake of their oleaginous seeds. It. must not, therefore, be come back upon again for sixyears, if fine crops be desired. The double ploughing which it requires effectuallycleans the ground. See Oils, Unctuous.
COMB, the name of an instrument made of a thin plate either plane or curved of wood,horn, tortoise-shell, ivory, bone, or metal, cut out upon one or both of its sides or edges,into a series of somewhat long teeth, not far apart; which is employed for disentangling,laying parallel and smooth the hairs of man, horses, or other animals. .
A thin steel saw bow, mounted in an iron or wooden handle, is the implement usedby the comb-maker to cut the bone, ivory, and wood into slices of from a twelfih to aquarter of an inch thick, and of a size suitable to that of the comb. The pieces oftortoise-shell as found in commerce are never flat, or, indeed, of any regular curvature,such as the comb must have. They are therefore steeped in boiling water sufficientlylong to soften them, and set to cool in a press between iron or brass moulds, which im-part to them the desired form which they preserve after cooling. After receiving theiroutline shape and curvature, by proper fiat files or fine rasps, the place of the teeth ismarked with a triangular file, and then the teeth themselves are cut out with a doublesaw, composed of two thin slips of tempered steel, such as the main-spring of a watch,notched with very fine sharp teeth. These slips are mounted in a wooden or iron stockor handle, in which they may be placed at different distances, to suit the width of thecomb-teeth. A comb-maker, however, well provided in tools, has an assortment ofdouble saws set at every ordinary with. The two slips of this saw have their teeth indifferent planes, so that when it begins to cut, the most prominent slip alone acts, andwhen the teeth of this one have fairly entered into the comb, the other parallel bladebegins to saw. The workman, meanwhile, has fixed the plate of tortoise-shell or ivorybetween the flat jaws of two pieces of wood, like a vice made fast to a bench, so thatthe comb intended to be cut is placed at an angle of 45° with the horizon. He now sawsperpendicularly, forming two teeth at a time, proceeding truly in the direction of the firsttracing.
A much better mode of making combs is to fix upon a shaft or arbor in a lathe a se-ries of circular saws, with intervening brass washers or discs to keep them at suitable dis-tances; to set in a frame like a vice, in front of these saws, the piece of ivory or horn tobe cut; and to press it forward upon the saws at an angle of 45 degrees, by means of aregulated screw motion. When the teeth are thus cut, they are smoothed and polishedwith files, and by rubbing with pumice-stone and tripoli.
Mr. Bundy, of Camden Town, obtained a patent so long ago as 1796, for an apparatusof that kind, which had an additional arbor fitted with a series of circular saws, or ratherfiles, for sharpening the points of the comb-teeth.
More recently, Mr. Lyne has invented a machine in which, by means of pressure, twocombs are cut out at once with chisels from any tough material, such as horn or tortoise-shell, somewhat softened at the moment by the application of a heated iron to it. Thepiece of horn is made fast to a carriage, which is moved forward by means of a screwuntil it comes under the action of a ratchet-wheel, toothed upon a part of its circum-ference. The teeth of this wheel bring a lever into action, furnished with a chisel orknife, which cuts out a double comb from the fiat piece, the teeth of which combs areopposite to each other. By this means, no part of the substance is lost, as in sawingout combs. The same carriage may be used, also, to bear a piece of ivory in the hardstate toward a circular saw, on the principles above explained, with such precision, thatfrom 80 to 100 teeth can be formed in the space of one inch by a proper disposition ofthe tool.
Bullocks’ horns, after the tips are sawed off, are roasted in the flame of a wood fire,till they are sufficiently softened ; when they are slit up, pressed in a machine betweentwo iron plates, and then plunged into a trough of cold water, whereby they are hard-ened. A paste of quicklime, litharge, and water is used to stain the horn to resembletortoise-shell. See Horn.
COMBINATION ( Combinaison , Fr.; Verbindung , Germ.) ; a chemical term whichdenotes the intimate union of dissimilar particles of matter, into a homogeneous-look-ing compound, possessed of properties generally different from those of the separateconstituents.
COMBUSTIBLE (Eng. and Fr.; Brennsloff. Germ.) ; any substance which, exposed inthe air to a certain temperature, consumes spontaneously with the emission of heaand light. All such combustibles as are cheap enough for common use go under -name of Fuel ; which see. Every combustible requires a peculiar pitch of tempe rato be kindled, called its accendible point. Thus phosphorus, sulphur, hydrogen, carreted hydrogen, carbon, each lakes fire at successively higher heats. -
COMBUSTION (Eng. and Fr.; Verbrcnnurtg , Germ.) results in common cafrom the mutual chemical reaction of the combustible, and the oxygen of the atmosphere