In the actual operations of blasting, definite rules for the proportioning of the charges are rarely observed, and although the blasts made by a skilful miner seldom fail to do their work, it is a common fault that too much, rather than too little, explosive is used. The high explosives are specially liable to be wasted, probably through lack of appreciation of their power as compared with that of black powder. Among the indications of excessive charges are the production of much finely broken rock or of crushed and splintered rock around the bottom of the hole, and excessive displacement or projection of the rock broken by the blast. In beginning any new piece of work, such waste may be avoided or reduced by making trial shots with different charges and depths of hole, and noting the results; also by letting contracts under which the workmen pay for the explosive. In surface rock excavation the location and determination of the depth of the holes and the quantity of explosive used, are occasionally put in charge of one or more skilled men, who direct the work and are responsible for the results obtained.
Blasting in surface excavations and quarries is sometimes done on an immense scale--called "mammoth blasting." Shafts are sunk, or tunnels driven, in the mass of rock to be blasted, and, connected with them, a number of chambers are excavated to receive the charges of explosive. The preparation for such blasts may occupy months, and many tons of gunpowder or dynamite are at times exploded simultaneously, breaking or dislodging thousands, or even hundreds of thousands, of tons of rock. This method is adopted for getting stone cheaply, as for building macadamized roads, dams and breakwaters, obtaining limestone for blast furnace flux, and occasionally in excavating large railway cuttings. It is also applied in submarine blasting for the removal of reefs obstructing navigation, and sometimes for loosening extensive banks of partly cemented gold-bearing gravel, preparatory to washing by hydraulic mining.
AUTHORITIES.--For further information on drilling and blasting see:--Callon, _Lectures on Mining_ (1876), vol. i. chs. v. and vi.; Foster, _Text-book of Ore and Stone Mining_, (1900), ch. iv.; Hughes, _Text-book of Coal Mining_ (1901), ch. iii.; H.S. Drinker, _Tunnelling, Explosive Compounds and Rock Drills_ (1878); M.C. Ihlseng, _Manual of Mining_ (1905), pp. 596-696; Köhler, _Der Bergbaukunde_ (1897), pp. 104-208; Daw, _The Blasting of Rock_ (1898); Prelini, _Earth and Rock Excavation_ (1905), chs. v., vi. and vii.; Gillette, _The Excavation of Rock_ (1904); Guttmann, _Blasting_ (1892); Spon's _Dictionary of Engineering_, art. "Boring and Blasting"; Eissler, _Modern High Explosives_ (1893), pts. ii. and iii.; Walke, _Lectures on Explosives_ (1897), chs. xix.-xxii. Also: _Proc. Inst. Civ. Eng._ (London), vol. lxxxv. p. 264; _Trans. Inst. Min. Eng._ (England), vols. xiv., xv. and xvi. (arts, by W. Maurice), vol. xxvi. pp. 322, 348, vol. xxiv. p. 526 and vol. xxv. p. 108; _Trans. Amer. Soc. Civ. Eng._, vol. xxvii. p. 530; _Trans. Amer. Inst. Min. Eng._, vol. xviii. p. 370, vol. xxix p. 405 and vol. xxxiv. p. 871; _South Wales Inst. Eng._ (1888); _Jour. Ass. Eng. Socs._, vol. vii. p. 58; _Jour. Chem. Met. and Mining Soc. of South Africa_, August 1905; _School of Mines Quarterly_, N.Y., vol. ix. p. 308; _Colliery Guardian_, April 15, 1898, and February 6, 1903; _Mines and Minerals_, February 1905, p. 348, January 1906, p. 259, and April 1906, p. 393; _Eng. and Mining Jour._, April 19, 1902, p. 552; _The Engineer_, February 24, 1905; _Elec. Rev._, June 9, 1899; _Eng. News_, vol. xxxii. p. 249, and August 3, 1905; _Gluckauf_, September 28, 1901, and July 5, 1902; _Österr. Zeitschr. f. Berg- u. Hüttenwesen_, May 18, 25, 1901, April 18, 1903 and November, 18, 1905; _Annales des mines_, vol. xviii. pp. 217-248. (R. P.*)