848 ____________________________________________________________________________________________________________________ THE COLLIERY GUARDIAN. April 25, 1913. __________________________________ small steam engines. One 40 brake horse-power motor drives a three-throw pump underground, and has replaced a direct-current machine, which required a separate generator at the surface. A 15 brake horse- power motor drives a crosscut saw and a small saw bench for cutting mining timber into lengths, making sleepers, &c. Current is also supplied to a Simplex coal- cutter with a motor of 20 brake horse-power. No. 5 Pit. There is no transforming station at this pit. The high-tension current is taken direct from the power station bus bars down the shaft, where it drives a motor of 180 brake horse-power operating a main-and-tail haulage gear (about a mile from the shaft inset), a 70 brake horse-power haulage gear and a centrifugal pump of 25 brake horse-power, the current for the latter being transformed to 600 volts on the spot. Arrangements are also being made for the installation of a 40 brake horse-power main-and-tail haulage gear, a 20 brake horse-power hoist for winding coal from a lower level, and a small compressed-air hammer drill plant. No. 7 Pit Sub-station. time the cost per unit is made up as follows, the figures being for the half-year ending December 31, 1912 :— £ s. d Wages ... ... ... ... ... ... 223 4 0 Fuel, 1,506 tons of slack at 6s. per ton ... 451 16 0 Stores ________________________________ 40 0 0 Depreciation and interest on the total outlay on the power station and transmission lines, at 10 per cent, on .£13,445 ________ 672 0 0 Total _____________________£1,387 0 0 ___________ Total units_____________________ 337,000. Cost per unit ______________ O‘987d. Normal load... ... about 350 kw. Load-factor ... ... ... 15 to 20 per cent. Advantages Derived. The advantages derived from the adoption of electricity may be summarised as follows:—(1) The colliery consumption has been reduced by at least 1| per cent., say 6,875 tons; (2) some 25 horses have been dispensed with underground; (3) a great reduc- tion in labour has resulted from the substitution of mechanical for horse haulage; (4) the Lancashire boilers no longer required (owing to the conversion of THE INFLUENCE OF INCOMBUSTIBLE DUSTS ON THE INFLAMMATION OF GASEOUS MIXTURES. Third Report of the Explosions in Mines Committee. (Continued from page 812.) Mallard and Le Chatelier’s Experiments. MM. Mallard and Le Chatelier, in their paper “ Du role des poussieres de houille dans les accidents de mines” (Annales des Mines, 1882), call attention to the peculiar properties of Abel’s firedamp—that a 2*5 per cent, mixture with air gave a barely perceptible cap on a lamp-flame, while a 3*5 per cent, mixture was explosive—properties which they consider to be “ inconciliables entres elles.” They also suggest the possibility that, inasmuch as Abel relied on an injector for drawing in air, the introduction of dust would reduce the efficiency of the injector and thereby give a richer gas-mixture than was anticipated. They give, however, what they consider to be a “ confirmation ” of Abel’s results with incombustible One 50 kw. transformer supplies current for a 25 brake horse-power turbine pump at the Five-foot level, at a depth of 257 ft. from the surface. A small feeder of water (chiefly from the shaft garlands), is dealt with at the Old Park level (408 ft. from the surface) by an hydraulic motor driven from the turbine pump rising main, which raises the water to the main lodge room. | No. 8 Sub-station. Three 50 kw. transformers, shortly to be replaced by two of 100 kw. capacity, supply current on the surface for two 20 brake horse-power motors for driving the screening machinery, and underground for one 120 brake horse power main endless haulage, two 30-horse power auxiliary main-and-tail haulages, and one 10-horse power portable main-and-tail haulage. A portable compressor and hammer drill equipment have recently been installed and other small haulages are in contemplation. The existing transformers will be used underground where required. I No. 9 Pit. | Arrangements for conveying the current to the company’s pits at Hednesford are in progress. The overhead bare wires will be connected through a switch on the surface to the main shaft cable. The current will be transformed to 600 volts, and used for haulage, heading, and coal-cutting purposes. Cables. The cables for the medium pressure are three-core bitumen-insulated throughout, and paper-lead covered, and the high-tension cables are double-armoured, with steel tape and wire. Lighting. In addition to the foregoing plant, lighting trans- formers are placed underground at important junctions and in some cases supply current on the surface. Cost of Installation. The following is a summary of the cost of the entire installation:— Power-station and Transmission Lines. £ s. d. £ s. d. Power - house, boiler - house, buildings, boiler - seatings, engine-foundations, &c...... 4,000 0 0 .... Two 200 kw. steam alternators 2,500 0 0 One 500kw. steam alternator... 2,574 0 0 Switchboards and fittings ...... 520 0 0 Three boilers, pipework, feed- pumps, superheaters, feed- water heater, &c............ 3,289 0 0 ............... Transmission lines to connect sub-stations .................. 562 0 0 __________ ----------- 13,445 0 0 Sub-stations Adapting old buildings at Nos. 3 and 8 pits, and building new houses at Nos. 2 and 7 pits, say ................... 200 0 0 Transformers................. 1,167 0 0 Switchboards and fittings, cables, &o.................. 2,059 0 0 Motors, haulage gears, pumps, &c......................... 3,888 0 0 Labour and excavation for motor-houses, laying cables, &c_________............................ 500 0 0 ___________ -----------7,814 0 0 Total capital outlay.... £21,259 0 0 It may be pointed out that in certain cases additional steam power would have been necessary to carry out what is now being done electrically. Cost of Generating Power. It is interesting to note the cost of generation, which compares favourably, even in the case of a comparatively small plant, with the cost of buying current from a public supply company. There are undoubted advantages in the latter method, and had there been such a company existing from which to buy power, the pros and cons would have been seriously considered. At the present * steam to electric power) are being utilised at other pits to supersede old egg-ended boilers, thereby reducing labour and consumption; (5) the current is available underground for further extensions in the way of auxiliary haulage, coal-cutting, &c., and for lighting up important stations, which, if not actually economical, is more convenient and safer. The annual saving effected is shown in the following: £ s. d. £ s. d. 1,546 0 0 650 0 0 1,562 0 0 ___________ 2,212 0 0 662 0 0 ___________ ----------- 1,550 0 0 500 0 0 250 0 0 100 0 0 £3,946 0 0 The total saving thus represents about 18j per cent. • interest on the capital outlay, apart from any saving { derived from the use of portable compressor plant and j power-drills, which have fully justified their adoption' during the short time that they have been in use. Colliery consumption, 6,875 tons at 4s. 6d. per ton ............ 25 horses, less at 10s. each for fodder, &c., per week ........ 50 boys at 2s. 6d. each = £6 5s. per day, or for year of 250 days ... Less wear and tear on ropes, hauliers’ wages, &c. (10 men at 5s. per day, or for year of 250 days), say ____.................... Reduction in hauliers due to the substitution of main-and-tail for endless haulage .......... Substitution of mechanical for hand-sawing of timber........ Screen-engine boys, &c.......... Total annual savin?...... General Surface Plan of the Electrical Installation at the Cannock Chase Colliery. . (Scale: Approximately 2| in. to the mile). powders. Their experiments can be described shortly as follows :— A vertical glass tube l‘5O m. high and 7 cm. in diameter, was traversed by a very gentle ascending current of a mixture of air and coal gas. The flame of a Bunsen burner was allowed to play across the upper opening, occupying about one-third of the cross-section. The gas mixture on coming in contact with the Bunsen burner flame surrounded it with a large blue aureole. Dusts were then introduced either at the top of the tube, by letting them fall through the flame of the Bunsen burner, or through the bottom of the tube, when they were carried up in suspension in the current of gas and air. Mallard and Le Chatelier’s account of the results they obtained is as follows:— “ When the dust entered at the lower end of the tube, it did not produce any particular phenomena, the flame did not descend in the tube, and there was, as before, no inflammation of the gaseous mixture except around the Bunsen burner flame. But when the dusts fell through the upper portion of the tube, they were brought to incandescence in traversing the Bunsen flame, and remained incandescent during the whole time of their descent in the tube. The little aggregations which they made in falling were surrounded by a very pale blue flame, which travelled down the tube with the dust but without ever completely filling its cross-area. If the dusts were heated in a platinum crucible