Hanging fire may be due to a cut, broken or damaged powder fuze, which may smoulder for some time before communicating fire to the charge. “Miss-fires,” which also are of not infrequent occurrence with both ordinary and electric fuzes, are cases where explosion from any cause fails to take place. After waiting a sufficient length of time before approaching the charged hole, the miner carefully removes the tamping down to within a few inches of the explosives and inserts and fires another cartridge, the concussion usually detonating the entire charge. Sometimes another hole is drilled near the one which has missed. No attempt to remove the old charge should ever be made.
High tension electricity, generated by a frictional machine, provided with a condenser, was formerly much used for blasting. The bare ends of the fuze wires in the detonating cap are placed say 1⁄8 in. apart, leaving a gap across which a spark is discharged, passing through a priming charge of some sensitive composition. The priming is not only combustible but also a conductor of electricity, such as an intimate mixture of potassium chlorate with copper sulphide and phosphide. By the combustion of the priming the fulminate mixture in the cap is detonated. As these fuzes are more apt to deteriorate when exposed to dampness than fuzes for low-tension current, and the generating machine is rather clumsy and fragile, low-tension current is more generally employed. It may be generated by a small, portable dynamo, operated by hand, or may be derived from a battery or from any convenient electric circuit. The ends of the fuze wires in the detonating cap are connected by a fine platinum filament (fig. 11), embedded in a guncotton priming on top of the fulminating mixture, and explosion results from the heat generated by the resistance opposed to the passage of the current through the filament. Blasting machines are made in several sizes, the smaller ones being capable of firing simultaneously from ten to twenty holes. The fuzes must obviously be of uniform electrical resistance, to ensure that all the connected charges will explode simultaneously. The premature explosion of any one of the fuzes would break the circuit.
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.*)
BLAUBEUREN, a town of Germany, in the kingdom of Württemberg, 12 m. W. of Ulm, with which it is connected by railway. Pop. (1900) 3114. It is romantically situated in a wild and deep valley of the Swabian Alps at an altitude of 1600 ft. and is partly surrounded by ancient walls. Of the three churches (two Evangelical and one Roman Catholic) the most remarkable is the abbey church (Klosterkirche), a late Gothic building dating from 1465-1496, the choir of which contains beautiful 15th century carved choir-stalls and a fine high altar with a triptych (1496). The choir only is used for service (Protestant), the nave being used as a gymnasium. The town church (Stadtkirche) also has a fine altar with triptych. The Benedictine abbey, founded in 1095, was used after the Reformation as a school, and is now an Evangelical theological seminary. There are two hospitals in the town.
BLAVATSKY, HELENA PETROVNA (1831-1891), Russian theosophist, was born at Ekaterinoslav, on the 31st of July (O.S.) 1831, the daughter of Colonel Peter Hahn, a member of a Mecklenburg family, settled in Russia. She married in her seventeenth year a man very much her senior, Nicephore Blavatsky, a Russian official in Caucasia, from whom she was separated after a few months; in later days, when seeking to invest herself with a halo of virginity, she described the marriage as a nominal one. During the next twenty years Mme Blavatsky appears to have travelled widely in Canada, Texas, Mexico and India, with two attempts on Tibet. In one of these she seems to have crossed the frontier alone in disguise, been lost in the desert, and, after many adventures, been conducted back by a party of horsemen. The years from 1848 to 1858 were alluded to subsequently as “the veiled period” of her life, and she spoke vaguely of a seven years’ sojourn in “Little and Great Tibet,” or preferably of a “Himalayan retreat.” In 1858 she revisited Russia, where she created a sensation as a spiritualistic medium. About 1870 she acquired prominence among the spiritualists of the United States, where she lived for six years, becoming a naturalized citizen. Her leisure was occupied with the study of occult and kabbalistic literature, to which she soon added that of the sacred writings of India, through the medium of translations. In 1875 she conceived the plan of combining the spiritualistic “control” with the Buddhistic legends about Tibetan sages. Henceforth she determined to exclude all control save that of two Tibetan adepts or “mahatmas.” The mahatmas exhibited their “astral bodies” to her, “precipitated” messages which reached her from the confines of Tibet in an instant of time, supplied her with sound doctrine, and incited her to perform tricks for the conversion of sceptics. At New York, on the 17th of November 1875, with the aid of Colonel Henry S. Olcott, she founded the “Theosophical Society” with the object of (1) forming a universal brotherhood of man, (2) studying and making known the ancient religions, philosophies and sciences, (3) investigating the laws of nature and developing the divine powers latent in man. The Brahmanic and Buddhistic literature supplied the society with its terminology, and its doctrines were a curious amalgam of Egyptian, kabbalistic, occultist, Indian and modern spiritualistic ideas and formulas. Mme Blavatsky’s principal books were Isis Unveiled (New York, 1877), The Secret Doctrine, the Synthesis of Science, Religion and Philosophy (1888), The Key to Theosophy (1891). The two first of these are a mosaic of unacknowledged quotations from such books as K.R.H. Mackenzie’s Royal Masonic Encyclopaedia, C.W. King’s Gnostics, Zeller’s Plato, the works on magic by Dunlop, E. Salverte, Joseph Ennemoser, and Des Mousseaux, and the mystical writings of Eliphas Levi (L.A. Constant). A Glossary of Theosophical Terms (1890-1892) was compiled for the benefit of her disciples. But the appearance of Home’s Lights and Shadows of Spiritualism (1877) had a prejudicial effect upon the propaganda, and Heliona P. Blavatsky (as she began to style herself) retired to India. Thence she contributed some clever papers, “From the Caves and Jungles of Hindostan” (published separately in English, London, 1892) to the Russky Vyestnik. Defeated in her object of obtaining employment in the Russian secret service, she resumed her efforts to gain converts to theosophy. For this purpose the exhibition of “physical phenomena” was found necessary. Her jugglery was cleverly conceived, but on three occasions was exposed in the most conclusive manner. Nevertheless, her cleverness, volubility, energy and will-power enabled her to maintain her ground, and when she died on the 8th of May 1891 (White Lotus Day), at the theosophical headquarters in the Avenue Road, London, she was the acknowledged head of a community numbering not far short of 100,000, with journalistic organs in London, Paris, New York and Madras.