A Treatise On The Principles And Practice Of Dock Engineering

HAULAGE AND TRACTION. 87 Gunpowder is a mixture of sulphur, nitre, and charcoal. It exerts an explosive force of from 18 to 40 tons per square inch, and weighs about 62^ Ibs. per cubic foot. For biasting purposes the lower power is used, and a cubic yard of quarry rock requires a charge of from | Ib. to 2 Ibs., according to nature and position; in tunnels and shafts as much as 6 Ibs. has been used. A formula given by Haswell for computing the quantity required is— F Charge in Ibs. = — , 0 x’ where I is the length of the line of least resistance in feet, and x a factor ranging from 25 for limestone to 32 for granite. The line of least resistance should not exceed one-half the depth of the hole. Nitro-glycerine results from the action of nitric and sulphuric acids upon glycerine. The addition of a granulat absorbent constitutes dynamite. This absorbent may be either inert or, in itself, an explosive. Dynamite, containing 75 per cent, of nitro-glycerine, has from four to six times the explosive force of gunpowder. Gun cotton is cotton dipped in a mixture of nitric and sulphuric acids. Tonite is gun cotton, in a finely divided state, mixed with nitrate of barium. The power of tonite may be said to be equal to that of dynamite, but the effect is somewhat less shattering. Haulage and Traction.—The question as to the relative merits of loco- motives and stationary winding engines for the haulage of excavated material from a lower to a higher level, depends entirely upon local circum- stances. Where there is ample space for the comparatively flat incline upon which locomotive traction is practicable that method is, generally speaking, preferable on the grounds of economy in working and of saving in time. The waggons can be conveyed direct from the excavator to the tipping station, whereas with the winding engine there are at least two breaks in the journey—one at the foot of the incline, where the waggons have to be connected with the hauling apparatus, either singly or in small detached groups, and the other at the summit, where they have to be disconnected and coupled up again. In the former case, under convenient circumstances, one locomotive may serve all requirements, both taking the waggons to the tipping station and bringing them back again. In the latter instance two locomotives, in addition to the winding engine, are absolutely essential— one working at the higher and the other at the lower level. Winding engines can, however, be satisfactorily employed where space is much restricted, since the incline may practically be made at any angle and as steep as is considered desirable. A slope of about 1 in 20 represents the critical pitch at which traction by locomotives begins to löse its superior efficiency. A very steep pitch throws considerable strain upon the working parts; and, indeed, in any case, it is advisable to arrange a triangular- shaped siding in order that the engines may be reversed from time to time.