Cracking

“ The explosion of the cap caused a sharp crack, and I was told that the tutor of the college remarked, "What an extraordinary thing it is, Mr. Darwin seems to spend hours in cracking a horse-whip in his room, for I often hear the crack when I pass under his windows." ”

“ Accompanying the cracking in many instances there seemed, according to one observer, "a blowing out of the earth, bringing up coal, wood, sand, etc., accompanied with a roaring and whistling produced by the impetuosity of the air escaping from the confinement... trees being blown up, cracked and split, and falling by thousands at a time. ”

“ The principles on which it depends are, that glass is a material breaking in every direction with a conchoidal fracture, and that the vibrations which would have caused cracking or fracture are checked by the support of the fixed centre-punch in close contiguity with the part to be broken off. ”

“ When selecting a paper for a whitewashed wall or ceiling, take a pattern which feels soft and pliable. Papers which crackle or rattle when crumpled in the hand are liable to crack. Papers which stretch or expand the most when wet are the most apt to crack; because when they dry and shrink the pull is so great that the fibers give away, if great care is not taken in putting it on. Cracking may be the fault of the paper hanger. He may use his paste too thick, or too thin, or put on too much or too little. ”

“ The circular form offers the least resistance to wind pressure, and for a given height and sectional area requires less material to secure stability than the octagonal and still less than the square; on the other hand, there is more liability to cracking. Brick is the material commonly used, but many chimneys are now made of iron or steel. Reinforced concrete is also employed. ”

“ The crack of the heavy carter’s whip differs from that of the coachman’s lighter one. There is the single crack, the double or back and fore crack, and the multiple crack, this last being like the dancing noise produced by those alarming crackers placed by mischievous urchins on a Queen’s Birthday night under the garments of terrified young women. There is the encouraging crack, supposed to cheer the horse on his way ”

“ Their commonest occasion is in the ascent of cracks, when the outward side-pull of the hand against the inside edge of the crack is set against the upward thrust from our foothold or knee-jam in the crack below, and our balance technique is occupied in compensating between them. ”

“ The streets however are nasty.
But it looks, I suppose, better than it smells—crack, crack—crack, crack—what a fuss thou makest!—as if it concerned the good people to be informed, that a man with pale face and clad in black, had the honour to be driven into Paris at nine o'clock at night, by a postillion in a tawny yellow jerkin, turned up with red calamanco—crack, crack—crack, crack—crack, crack,—I wish thy whip—
—But 'tis the spirit of thy nation; so crack—crack on. ”

“ To burst is to break by pressure from within, as a bombshell, but it is used also for the result of violent force otherwise exerted; as, to burst in a door, where the door yields as if to an explosion. To crush is to break by pressure from without, as an egg-shell. To crack is to break without complete severance of parts; a cracked cup or mirror may still hold together. Fracture has a somewhat similar sense. In a fractured limb, the ends of the broken bone may be separated, tho both portions are still retained within the common muscular tissue. ”

“ Fine cracks resulting from shrinkage on the surface of glazed pottery, concrete, or other material. The admired crackle in some Oriental potteries and porcelains is crazing produced in a foreseen and regulated way. In common pottery it is often the result of exposure to undue heat, and the beginning of disintegration.
Crease (?) , n. (Lacrosse) The combination of four lines forming a rectangle inclosing either goal, or the inclosed space itself, within which no attacking player is allowed unless the ball is there; -- called also goal crease. ”

“ Just then—Crack! crack! Two—four—a dozen musket and pistol shots, followed by such a chorus of yellings and howlings and unearthly laughter! The creature that held me seemed startled—relaxed his grasp slightly. At that moment a dark arm was passed before my face, there was a blinding flash, a yell, and I fell to the ground released from the clutch of my opponent. I remember nothing more. Overcome by pain, fatigue, terror, and the noxious vapors of that vile ravine, my senses abandoned me, and I swooned away. ”

“ When you have done the best you can to get the general form, proceed to finish, by imitating the texture and all the cracks and stains of the stone as closely as you can; and note, in doing this, that cracks or fissures of any kind, whether between stones in walls, or in the grain of timber or rocks, or in any of the thousand other conditions they present, are never expressible by single black lines, or lines of simple shadow. A crack must always have its complete system of light and shade, however small its scale. ”

“ In Plate V, page 112, are given six figures representing various cracks and fissures. No. 1111 represents the cracks in the glaze of Japanese pottery, magnified. No. 2 shows the mud cracks on the edge of a lake, to the extent of two feet. No. 3 is a series of cracks in an asphalt pavement, covering about two feet. No. 4 shows the form of cracks in the surface of a mesa in Arizona, the result of the summer heat, the length being about ten feet. No. 5 is a tracing from a drawing by Professor W. H. Pickering showing cracks in the lunar crater Eratosthenes, with an extent of fifty-five miles. ”

“ Imagine forces of some kind, acting laterally, to compress those layers. There will be corrugations, sometimes actual fractures, the two sides of which, sliding one against the other, will be either raised or depressed. Faults is the name which we give to the fractures that penetrate the terrestrial shell and separate two masses of rock, one of which slides over the plane of fracture. The fault, therefore, reveals an edge, a lower lip produced by the subsidence of the soil, and an upper lip produced by an elevation. ”

“ Cracks arising from contraction never converge to a common centre, and when not connected with another crack they taper to a point. They begin at indefinite places and end in an equally indefinite manner. That there should be a common resemblance in cracks due to contraction109 is evident as they arise from a shrinking of the surface. The most ancient deposits, millions of ages ago, reveal mud cracks differing in no respect from those found to-day. We subjoin a few forms of cracks from various surfaces, to show their essential resemblance. ”

“ In difficult crack climbing the extent to which pressure, the jamming of a leg, the touch of a calf or knee, or the twisting of a hand or forearm can be used to ease the muscular strain must be learned by practice. A fist or finger may be hooked in a smooth rift, or a foot slanted into a crack, with only friction attachment, and a slight twist to arm or leg converts either into a secure lever for lifting the weight. The clenching of the fist or the tightening of the muscles of a jammed forearm, or even the inflation of the chest, may at need serve the same purpose. ”

“ If the grain side of a belt is the outside when on the pulleys, and a crack should consequently start, the destruction of the belt proceeds rapidly, because the line of crack is the weakest part of the belt, and the belt has less elasticity as a continuous body, and more at the line of crack. ”

“ When a vertical or sloping crack in a slab gets too small even to admit a finger, and all other holds are lacking, they force the point of the pick into the crack above their heads, and give a slight outward and upward twist to the shaft with the wrist, so that the point of the pick and its square edges are jammed slantwise and upwards in the crack. Holding the shaft rigid in this position, they then raise their weight by sheer strength inside the bent arm which holds the shaft, at the same time using whatever friction-holds they can find for their feet to help them. ”

“ You ignite the first cracker and the flash fires the fuse of the second, and so on, until, after a series of crackling detonations, the whole bunch has exploded, and nothing survives but a few torn and scattered bits of paper, blackened with powder. ”

“ On each side of the crack a small horizontal furrow is burned or cut into the wall, leaving the horn for about 1/4 inch on each side of the crack intact. This provides a groove for the ends of the clamping-nail to rest in, and brings them flush with the outer surface of the wall. The nail is then driven carefully home through the crack, and the pointed end grasped by the farrier's pincers. The edges of the crack are then drawn tightly together, and the nail firmly clenched. ”

“ If a crack does not form, touch the hot place with the cold end of the nail. If no success is obtained, try the other end of the scratch. If failure still pursues the operator, let him make another cut on the opposite side of the tube and try again. In general, the tube will yield the first or second time the hot drop of glass is applied. Never apply the drop at the centre of the scratch, or a ragged crack, which may run in any direction, will result. Very often, with a large tube, the crack formed by a successful operation will only extend a short distance. ”

“ Let us imagine a solid prism ABCD fastened into a wall at the end AB, and supporting a weight E at the other end; understand also that the wall is vertical and that the prism or cylinder is fastened at right angles to the wall. It is clear that, if the cylinder breaks, fracture will occur at the point B where the edge of the mortise acts as a fulcrum for the lever BC, to which the force is applied; the thickness of the solid BA is the other arm of the lever along which is located the resistance. ”

“ CAUSE AND PREVENTION OF CRACKS.—Cracks in cement walks are of two kinds, fractures caused by any one of several construction faults and which reach through the surface coating or through both surface and base, and hair cracks which are simply skin fractures. Large cracks are the result of constructive faults and one of the most common of these is poor foundation construction; other causes are poor mixing and tamping of the base, too large blocks for thickness of the work, failure to cut joints through work. ”

“ To mend a crack in clay that is only partially dry, put a little slip into the crack and then work in, with a modelling tool, clay of the consistency of the piece. If, after drying longer, the piece cracks again—a long, deep crack, that goes through to the inside—there is no way to mend it except by cutting the clay out on either side for quite a space beyond the crack, brushing both sides with slip, and filling in with clay as nearly as possible the consistency of the piece. ”

“ The crack may indicate a cracked driver or a crack one, according as it is the passers-by or the driver himself who forms the opinion, and it is an obviously enviable accomplishment which many can manage with their left hand. ”

“ In this case only tensile normal stresses act on the rectangular pair. One is a maximum, the other a minimum. After a crack has formed, the maximal stress and strain normal to the crack has been relieved, so that the former minimal normal tension along the crack becomes now the maximum. The next rupture will therefore be orthogonal to the first crack. The reason for this peculiar configuration is thus found by the methods of projective geometry. ”

“ That which occurred along this line was a differential movement and permanent displacement of the rock and earth on the two sides of a vertical crack. The principal displacement was not vertical, but horizontal. If one thinks of the land to the east of the crack as stationary, then the change may be described as a northward movement of the land west of the crack. If the land to the west be thought of as stationary then the land to the eastward moved toward the south. It is probable that both tracts shared in the movement, the eastern shifting toward the south and the western toward the north. ”

“ Where pain is not so great that relaxation of parts does not occur, one can, by gently moving an extremity in various directions—as in flexion, extension and lateral motion as well as by rotation—cause to be manifested this peculiar grating,—the friction of newly broken bone. This is known as true crepitation. Where the subject, suffering phalangeal fracture, manifests evidence of pain due to tensing the structures about a fractured part, one may anesthetize the parts by using about two cubic centimeters of a two per cent. solution of cocain upon the plantar nerves, proximal to the fracture. ”

“ From the fact that cracks once made in a building did not appear to extend under the repetition of shocks similar to the one that produced them, it has been inferred that buildings thus cracked acquire a degree of flexibility, and that, by providing cracks or joints between the parts of buildings which have different periods of vibration, some of the strain might be taken off from them, and they might be made more stable. ”

“ It follows from the above considerations, that if there be only one or only two lines of fracture they must gradually diminish and end somewhere, and that the dislocated ground must have at least one place of maximum disturbance towards which it bends down either in one or several directions. ”

“ But as any one on [253] looking at a broken pane of glass can readily determine whether the force came from without or from within by the direction of the fragments that still adhere, so in the chipped egg it is easy to perceive, by the projection of the pieces around the entire circlet, that the breaking force comes from within. And I myself, and many others with me besides, hearing the chick scraping against the shell with its feet, have actually seen it perforate this part with its beak and extend the fracture in a circle like a coronet. ”

“ When these crackers are fired, they will give a report at every turn of the paper. If there are to be a great number of bounces, the paper must be cut longer, or be joined after they are made. If, however, they are made very long before they are pinched, there must be a piece of wood, having a groove sufficiently deep to let in half the cracker, which will hold it straight, while it is pinching. ”