Concrete is a troublesome material in which to drill deep holes; it is a good plan to use water under pressure, with a wide flare bit, permitting a small copper waterpipe to be inserted nearly to the bottom of the hole, so that chips and dust are carried off before they can wedge the bit.
Plasticity may be defined as the property which many bodies possess of changing form under pressure, without rupturing, which form they retain when the pre-out rupturing, which form the retain when the pressure ceases, it being understood that the amount of pressure required, and the degree of deformation possible, will vary with the material.
A stream of water can be thrown vertically 103 ft. and horizontally 9** ft., with a pressure of 100 lb. at the nozzle and 1 3-8 in. diarn. The nozzle will discharge 674 gai. of water per minute. With a higher pressure, equivalent to a higher head, the amount discharged and the distance to which the water may be thrown will be increased.
Over 50,000,000 gal. of water are pumped out of the anthracite coal mines of Pennsylvania every day in the year. The exact average for 1905 was 633,000,000 gal. per day. Nearly 1,000 powerful engines, delivering from mine bottom to surface 500,000 gal. of water per minute, are required. Mines may be shut down and coal production suspended but the water flows on forever. The cost of removing it is one of the important items of expense that make up the price of anthaeite.
Whether a high-power or a low-power explosive is to be used in blasting, is dependent largely upon the use to which the rock is to be put, as well as upon the strength of the rock itself. Black powder, with its comparatively slow, heaving action, is used where the material is quite friable, as in mining coal or galena, or in excavating shale, hardpan, and similar material. A high-power explosive like dynamite is invariably used in tunnel-driving, shaft-sinking, and open-cut work in tough rock. It cannot be used for quarrying dimension as it shatters the rock.