Page:The American Cyclopædia (1879) Volume II.djvu/717

 BLASTING 697 always held that one who maliciously makes use of language calculated to have an evil ef- fect in sapping the foundations of society and of public order, may properly be punished as an offender against the state. But a fair dis- cussion in a decorous manner of any contro- verted point or doctrine of religious belief stands on very different ground, and is inno- cent; the evil motive being essential to this offence. Profane swearing is a species of blasphemy, but more lightly punished. BLASTING, the process of breaking rocks with explosive compounds. It is employed for break- ing stone from quarries for building purposes, for removing rocks from the surface of the earth, from the beds of watercourses, and from mines, and for the demolition of fortifi- cations, docks, and other works. It follows, therefore, that the process will vary consider- ably according to the object to be accomplished, and the differences in the material to be acted upon as to hardness, position, and mode of stratification. Until within a few years the only explosive compound used in blasting was gunpowder. It is not known when this agent was first used for this purpose, but as the Chi- nese were acquainted with its use as a projec- tile force in very early times, it is not improba- ble that they also used it in mining operations, which were carried on by them to a considera- ble extent long before the Christian era. In Eu- rope the Germans were probably the first to em- ploy it in mining. In making preparations for blasting, the first step is to examine the rock for the purpose of determining the size, location, and form of the cavity for the explosive mate- rial, and the amount of the latter necessary to overcome the resistance. In ordinary blasting operations, simple drill holes are usually fired, and may be so placed and combined in groups as to effect the displacement of great masses of rock ; but in large operations mines are ex- cavated for the introduction of the explosive. In either case one of the principal operations is the boring or drilling of the rock. Drills of various forms are employed short and light for working by hand, larger and longer when they are to be driven with a sledge. These drills are made by flattening the end of a steel bar, and drawing it to a blunt, outwardly curved edge, which should be from one eighth to one fourth of an inch longer than the di- ameter of the shaft. The included angle at the edge should be from 70 to 90. This part of the drill is called the bit. Other drills, called jumpers, are made longer and of a different form, and are intended to be driven by the force of their own gravity. The jumper is made of a bar of steel or iron from 5 to 8 ft. long, with a bulbous enlargement rather nearer one end than the other. The bit, which is of steel, has usually the same form as in the hand drill,, but sometimes has two cutting edges, formed at right angles with each other. In using the jumper from two to four men are employed, who simply raise it to the proper height and let it fall, giving it at the same time a sufficient rotary motion to cause it to cut a chip from a bench left by the preceding stroke. The hole is usually commenced with one end of the drill and finished with the other. Some drills which are propelled by their own weight are made very heavy and raised by steam power. Other drills, the most notable among which are the Burleigh, Ingersoll, Wood, Hotch- kiss, and Gardner (see BOEING), are mounted on carriages and driven by steam or com- pressed air, which is delivered by means of pipes and stout hose capable of sustaining a pressure of from 60 to 80 Ibs. to the square inch. By the use of air in place of steam, the drill can be worked in chambers where the heat and moisture produced by the discharge of steam would be unendurable. Revolving tools worked on the principle of augers, with bits of various forms to suit the kind of work to be done, may be advantageously used in soft rock. The American diamond drill is a revolving tool which is driven by steam or compressed air. The bit is armed with black diamonds, which are so adjusted as to cut a free passage for the drill rod. It is much used in deep boring for artesian wells and for pros- pecting coal and other mines, but is said to be also well adapted to boring holes for blasting. Natural fissures in the rock are often taken advantage of to introduce powder, which is covered with dry sand, a communication being retained by means of a fuse. This is called a sand blast. For breaking down the huge blocks of native copper in the mines of Lake Su- perior, no other known method but shaking them by the sand blast would be effectual. Standing upon their edges in the veins, and entirely enclosed in solid rock, they are first uncovered along one of their sides by exca- vating a horizontal drift or gallery. Small cavities are then made behind the mass, along its upper edge, by repeated blasts in the tangled rock and copper. As these cavities are enlarged, more powder is introduced, till, if the mass be very large, several hundred pounds are spread in the crevice behind it, and fired at once ; and thus it is finally thrown over into the open space previously excavated. As the great labor in blasting consists in drilling the holea, which after all contain but a small quantity of powder, various plans have been devised for enlarging the cavity at the bottom. In calcare- ous rock this has been effected by the use of acids, which dissolve the stone. For other rocks a very ingenious process was invented by Mr. A. Stiokney, of Concord, N. H. After the hole (which should be not less than 3 in. in diameter) is bored to the depth of 5 or 6 ft., fragments of the best hard-wood charcoal are thrown into the bottom and ignited. A blast is then blown in from a portable bellows through a wrought-iron tube, to which is added at its lower extremity a tube of pla- tinum not less than a foot in length and half an inch in diameter. The lower extremity of this