November 10, 1916. THE COLLIERY GUARDIAN. 901 shorter one, or that intermediate coal supplies will be of greater advantage than supplies at the Panama Canal. The cost and class of coal, and facilities for coaling, must also largely affect the patronage of one station more than another, unless other considerations predominate in the direction of securing cargo; and on these condi- tions depend to what extent intermediate stations or ports en route east and west of the canal will retain patronage. It may here be mentioned that new coaling stations have already been arranged for on several routes via the Panama Canal. As to coal bunker supplies on other routes : via the Suez Canal there are the several Mediterranean ports, including Gibraltar, Algiers, Oran, Malta, and Port Said; then onwards beyond the Suez Canal are Suez, Aden, Colombo, Sabang, Singapore, etc.; vid the Cape of Good Hope are the Atlantic coaling stations of Madeira, Las Palmas, Teneriffe, St. Vincent (Cape Verde), then Cape Town, Durban, etc.; and vid COAL DUST EXPERIMENTS IN THE DERNE GALLERY.* During the year 1915 numerous experiments were carried on in the experimental gallery at Deme, to investigate further the minimum quantity of coal dust that is capable of propagating an explosion. One point established by these and earlier experiments is that, when an explosion has already attained complete development, the presence of 70 grms. of coal dust per cu. m. of air is sufficient to carry it on indefinitely, that is, presuming the dust to be composed of very fine particles of bituminous coal with not more than 10 per cent, of ash, and that is situated in positions where it can be easily reached by the explosion. More cor- rectly speaking, the experiments in question, therefore, Cape Horn coal supplies are available at the West Indies and the South American east coast ports. That coal from the United States will com- pete more extensively, on the west coast of South America and on the Pacific route east, with the supplies of Australia and Japan, there can be no doubt. Also, to retain markets at present held for English coal, but brought nearer to the United States by the Panama Canal, will call for improvements in coaling facilities, and a closer study of supplies and of return freights to be secured. Regarding the cost of coal, this must be affected by freights; and nitrate from Chili will afford the opportunity of return cargoes, particu- larly to the United States. Further, exten- sive resources of iron and copper ore are available in Chili, which can be shipped to Baltimore and New York, and will allow of low outward freights for coal. Already coal cargoes from Newport News to Panama provide tonnage for iron ore from Cuba for the return voyage to Baltimore. Some of the principal cargoes which passed through the canal dur- ! Bl ■ -g 1 1 -A / A! ■ KA L- •’ > • 'A; Fig. 4.—Goal Bunkering from Wharf Side with Portable Elevator. tions specified. If, however, the dust is merely lying quiescent—as is mostly the case when single shots are fired in the mine—a propagated explosion does not occur until the amount of dust reaches 400 grms. per cu.m., and even then the explosion is restricted at first to that portion of the gallery where this amount of dust is pre- sent. Only when the zone rich in dust exceeds 50 m. is the explosion capable of further propagation by smaller quantities of dust. The explosive capacity of coal dust from two seams in a Westphalian colliery was investigated, but in both cases the dust was comparatively safe, having an ash content of 20'5 and 35 per cent, respectively. Anti-Explosion Devices. Stone Dusting.—Further experiments were made with the stone dust barriers described in the last report (Colliery Guardian, Oct. 29, 1915, p. 874), for the pur- pose of checking results previously obtained. Concentrated Wet Zones.—The ordinary wet zones, produced by means of sprays connected with the water- ing mains, have proved inefficient in the cheeking of powerful coal dust explosions, and it was therefore con- sidered advisable to try the effect of concentrated wet zones, arranged and operated in a manner similar to the stone dust barriers. They are formed by storing water in considerable quantities at one or more points in the protective zone to be constituted. The water is stored in boxes, mounted in such a way as to be over- turned or destroyed by the force of an explosion. Numerous methods have been devised for facilitating the suspension and tilting of the boxes, the shape and dimen- sions of which have also received much attention; but these are points which can be left out of consideration until the fundamental problem has been solved, namely, what is the relative value of concentrated wet zones, and how much water is required. The general modus operandi of the concentrated wet zones is arranged on the lines that they shall place a large volume of water in the path of the explosion, sud- denly and at the critical moment. The devices must be operated by the shock of the explosion itself, and must therefore be arranged so that they can be acted upon by the pressure wave which precedes the flame of the explo- sion. The simplest way is to mount the water vessels in the gallery at such a height as not to interfere with the traffic; or they might be housed in a recess in the roof, and operated by a lever hanging down in the roadway and terminated there by a disc or plate exposed to the force, of the explosion. In the experimental gallery, the former method has been adopted, as being the more advantageous, and because a recess in the roof is impracticable. In practical mining, iron vessels will be advisable for holding the water; and these have also been occasion- ally used in the experimental gallery. Since, however, the vessels are always destroyed by the explosion, the general practice is to use wooden boxes, being simpler and cheaper. Their dimensions are: Length, 4ft.; width, llfin.; height, 10^in.; capacity, about 20 gals., to meet the conditions of the gallery. As a simple way of tilting the vessels, a | in. iron shaft was secured, by means of two strips of plate, along the central line of the bottom of the vessel, the projecting ends of the shaft being carried in eyes of two iron rods depending from a wooden beam across the roof. The vessel was held in the upright position by a lath, fastened at the centre to .am*. < ' -A' Fig. 5.—Discharging Collier “• Ulysses” at Cristobal Coaling Station (1916). ing the year ending June 1916 included nitrate, 894,000 tons; petroleum and crude oils, 341,000 tons; coal, 243,000 tons; sugar, 129,000 tons; timber, 90,000 tons; iron ore, 52,000 tons', and copper, 37,000 tons. There is little doubt that the Panama Canal, by open- ing up new routes, will add to the prosperity of several countries, which will, of course, include the Pacific coast of South America; also various projects have been proposed, and in some cases already proceeded with, to provide for developments at the West Indies—Barbados, Trinidad, Jamaica, and St. Thomas. The linking-up of the generating stations of the various electric works in the Metropolis is expected to economise enormously the cost of production, and to save some thousands of tons of coal annually, in addition to the different stations being able to assist each other in dealing with the heavy demands for current and continue the working where partial breakdowns have taken place. related to the problem of the amount of coal dust neces- sary to enable an explosion to attain complete develop- ment. The results of these investigations show that, when an explosive mixture is present at the face (or in the experimental gallery), its explosion produces such a violent impulse that the explosion is self-propagating, even when the amount of dust present is as low as 70 grms. per cu. m. of air. In the case of a purely coal dust explosion (without any firedamp), the development of the explosion depends largely on whether the igniting shot flame can reach the coal dust at once or not. If the coal dust be in a state of suspension in the air before the shot is fired, 80 grms. of dust per cu. m. will suffice to maintain an explosion, but only for a distance of a few metres, and without further propagation—for which at least 112 grms. of dust are necessary under the condi- * From Gliiekauf. the upper side of the box, and forked at the ends to engage with the supporting irons, so as to give way easily on the application of pressure, and allow the box to tilt. In all the tests the water boxes were destroyed, nothing but small splinters remaining after the explosion. The protective zone was formed in the ferro-concreted portion (15 m. long) of the gallery. This portion being of rectangular section, the water boxes could be arranged in the same way that they would be in practice, and 5| ft. above the floor. The first box was set up at 102 m. from the end of the gallery, and three others were installed at intervals of 2 m. beyond. Coal dust was strewn in the usual way all along the gallery, including the wet zone, but was stirred up in the front end of the gallery alone. In most cases the ignition was produced by a charge of 200 grm. of dynamite; but smaller explo- sions, in presence of firedamp, were induced by an electric igniter.