18 THE COLLIERY GUARDIAN. July 5, 1918. it can never exceed a predetermined value, and is usually somewhat lower than its maximum value. The arrangement is shown, in figs. 7 and 8, fed from the lighting system and battery respectively; but it is more satisfactory and cheaper to run direct from the lighting supply. When the supply voltage is 220 volts, some 20 to 30 pilots may be all run in series. They consist of two- volt lamps, with a current consumption of 0’5 ampere per lamp. In series with the lamps is placed a 32 c.p. 220-volt lamp, which limits the current through the system. It will be assumed that a circuit consists of 20 two- volt lamps, each taking 0’5 ampere, but all connected in series. The resistance of each lamp will be equal to the electromotive force divided by the current per lamp, £.e., = 4 ohms per lamp. The total resistance of the series would be 4 X 20 = 80 ohms. Also, the resist- ance of a 32 c. p. 220-volt lamp which takes about E 220 0*5 ampere is R=^ = -^ =440 ohms. Now, assuming that the whole series of lamps are in circuit with the 32 c.p. lamp, the current through the circuit and lamps will be equal to „ E 220 220 A.o (J= — = ——-—-=—_= 0 42 ampere, R 80440 520 so that, although the lamps will not be giving their full candle power, ample light will be furnished to indicate what is desired. It will I e seen from the connections of the switches relative to the individual lamps in figs. 7 and 8 that they may be used to short-circuit their respective lamps, i.e., the lamps will be glowing when the switches are open and dark when the switches are closed. It will also be obvious that any number may be extinguished without the current through the remainder exceeding the normal current of the lamps. The'success or otherwise of any system of pilot lights depends on the reliability of the methods employed. Any weak points may cause confusion when lights become extinguished without apparatus really being dead. The constant-current circuit, as indicated above, does not allow of an individual lamp burning out with- out extinguishing all the rest in that series, which will remain out until the defect has been attended to. The method thus provides that unless the lamps in a given series are all intact, the remainder refuse to operate. (To be continued.) EXTRACTING COAL PILLARS FROM FIERY SEAMS.* By R. H. Husband. The extraction of coal pillars (or working “brokens”) is a subject claiming the most careful attention from colliery managers in India, the thick coal seams being generally considered more favour- able to the adoption of some form of “ pillar ” working rather than the true “longwall” system. In this connection the very important question arises, namely, whether in any Indian coal mine where goaf packing has to be resorted to, it would not be much safer, more economical, and more in keeping with the ideals of modern mining practice to take out the pillars soon after their formation and follow up the 11 whole ” with the “broken,” rather than wait until the boundary is reached before extracting the pillars. The great object aimed at in applying the “pillar” system is to extract the whole, or as large a percentage as possible, of the coal without replacing it with arti- ficial packs and pack walls; and for this purpose the system is divided into two distinct operations, worked in the following numerical order: (1) The “whole” a saving under other heads of working costs that will in very many cases more than compensate for the cost of packing. In short, the proposal is simply to adopt the “following up ” system of “brokens” and completely pack the goaf behind commencing away from the shaft pillar. If goaf packing as a preventive can be successfully adopted after the workings have reached the boundary, there seems to be no reason why it should not be applied with even more success if commenced at the shaft end of the mine. As an example, let us assume a taking of 600 acres, coal to be won from a pair of shafts near the centre of the property; let us further assume that the coal is strong and at a fairly good depth, that a 20 per cent, extraction can only be made in the “whole” workings, and that the mine in general has all the disadvantages that combine to merit the term “ fiery.” Assuming that “brokens” will not be commenced until the boundary is reached, the first consideration after having completed the shaft equipment, arranged for the necessary ventilation and determined the size and shape of the shaft pillar, etc., is the size of the ordinary pillars. With strong coal, machine mining (punching machines) appears the best, but the machines can only be profitably worked if applied to Refcrcn.ces. D. Dem cos$ anti *v beating Shaft. IL Up Cast Shaft tS^^nirecLL-on- of air current. x ffir Crossing, H. Reg tiiauLo r, D D. Doors. JE.H. Electric Hauling Gta" THE CARBONISATION AND DISTILLATION OF PEAT. Messrs. C. Galaine and C. Houlbert recently sub- mitted a paper to the Paris Academie des Sciences on the carbonisation and distillation of peat, saw- dust, household refuse and other light organic products. The value of peat lies in the direction of dis- tillation rather than combustion, and on these lines it could supersede wood in the production of acetic acid, methylated spirit, ammonia and tar, the basis of so many dyes. In the process of distillation, peat, being a light material, requires larger retorts than coal, and of a design which facilitates the transmission of heat from the surface towards the centre. Experiments have shown that revolving retorts produce the best results. The apparatus devised and described by the authors is on the principle of the roasting appliances used for coffee, chicory, etc., but, of course, with the addition of a receiver for collecting the distilled vapour, the great object being to provide an apparatus com- plete in itself for continuous and all-round operation. This apparatus consists of six cylindrical retorts, each mounted on its own axis and capable of uniform rotation, whilst the individual cylinders are arranged in radial relation to a rotary central pivot, so that the retorts charged with peat can be entered into and withdrawn from a stationary semi-circular furnace in succession. When the apparatus is in operation there are always three retorts undergoing distillation in the furnace, the other three being outside—one condensing, another emptying, and the third re-charging. The distillation takes on an average about 40 minutes for retorts holding a ton of peat, and making six revolutions per minute. To enable the gas arising from the carbonised peat to pass out of the retorts, the hollow shaft of each is perforated so as to provide a passage from the inside of the retort to a collecting chamber in the axis of the pivot and thence to the stills for fractional distillations. The rotary movement of the retorts ensures rapid transmission of heat from the furnace, and as this heat acts on a very large surface, the peat is uni- formly carbonised in a short time at a relatively low temperature—a result which, it is claimed, is impos- sible to obtain by any other process. Extraction of Ammonia, Toluol, and Benzol. —The Ministry of Munitions has issued an Order regulating the production of gas. It applies to all gas works excepting those which possess only coal gas plants and have no means of scrubbing or washing their gas with oil or with tar. All gas works which have facilities must scrub the whole of their coal gas to the fullest possible extent for the extraction of ammonia, toluol, and benzol. Where a benzol recovery plant exists, scrubbing for toluol and benzol is to be effected with oil, and in other cases with tar. Regulations are also laid down dealing with the admixture of water gas with coal gas, limiting the extent of dilution by this means, and specifying the conditions under which the water gas shall be carburetted. Gas works unable to comply with the terms of the Order must notify the Ministry of Munitions, which will issue in- structions or directions to meet the special circumstances. Applications with reference to the Order should be ad- dressed to the Ministry of Munitions, Department of Explosives Supply, Storey’s-gate, S.W.I., and marked “ E. G. S.” working or formation of the pillars; (2) the “broken” working or the extraction of the pillars formed during the first or “whole” working. No hard and fast rule to meet all cases can be laid down to determine the exact size of pillar to be left for the “broken” working; usually from 20 to 25 per cent, is taken out by the “ whole ” drivings, leaving a balance of from 75 to 80 per cent, in the pillar to be extracted as soon as circumstances permit. In the North of England it is the usual practice to follow up the “whole” with the “broken,” leaving only such pillars as may be necessary to maintain the trunk roads for haulage and ventilation, etc., under prime strata, also always keeping about two or three rows of pillars between the “whole” and “broken” workings. The advantages of this procedure are generally well understood, but the difficult conditions under which coal seams are often found to occur in India prevent any such immediate extraction, and therefore special precautions must be taken to guard against (a) undue surface subsidence which may cause a heavy influx of water into the mine, also damage to large railway works and important buildings, etc.; (b) gob fires originated by the oxidation of com- bustible material which often forms an integral part of the fallen roof. There is also another source of danger which may not be associated with the “broken” working at all, i.e., in so far as its origin is concerned, namely, spontaneous combustion in the pillar itself. It would therefore appear that a real source of danger exists whichever method of extraction be adopted, unless a suitable preventive can be applied. Preventive Measures. Probably the best preventive to meet all require- ments is the complete stowage of the goaf, the only disadvantages to its application being the absence of suitable packing material at or within a convenient distance from the mine, and the extra cost involved in the operation of packing. In the first instance it may be remembered that wherever we have surface running water to guard against we may reasonably expect to find therein a sediment suitable for underground packing purposes. In the second instance the author is of opinion that the packing can be used in such a way as to effect * From a paper read before the Mining and Geological Institute of India, and published in the Transactions. Fig. 1.—Position of Main Engine Planes, Etc., for Working with Packing. -aw- -in- a driving of a certain width, that is, the time occupied in flitting the machines must be taken into account. This means correspondingly large pillars, but in view of the liability of the coal to spontaneous combustion, the bigger the pillar the greater the difficulty in getting to the seat of a fire. One is therefore com- pelled to resort to smaller pillars and narrower drivings (with hand labour), a method ill-suited to the class of labour available, and hindering the average output per person employed. During the period occupied in driving out to the boundary the working costs are mounting up. For instance, such a mine, for its efficient ventilation would probably require something like 200,000 cu. ft. of air per minute per 6 ft. thickness of seam, and by the time the boundary is reached there are exposed—for the exudation of occluded £ases and rubbing surface for the ventilation—an area equal to about 20,000,000 sq. ft. Hence a powerful fan with its duplicate parts will have to be installed; but out of the total ventila- tion produced only about 35 per cent, will actually be utilised at the working faces, the balance, viz., 65 per cent., being allowed to scale through holes in the stoppings to ventilate pillars that are lying idle. Again, every hole and corner of these back-bye places must be inspected daily and kept clean and in thorough repair by a large staff of labour (wastemen). Timber must be renewed where necessary, and every place not undergoing repairs must be securely fenced. A portion of the tram-lines must be left in to admit of these repairs being carried out satisfactorily. It may not be considered prudent to take out and carry forward the brick stoppings, as these may be required at any time to check or divert the air current in case of fire; hence extra rows of stoppings will be required for every new headway won out. The danger attend- ing an outbreak of fire, if not promptly dealt with, necessitates a series of small diameter water pipes con- nected either to the shaft pump column or to the rising main from the dips and arranged at convenient distances to quench fire if necessary. In addition, as many bricks and as much lime will have been used for extra stoppings as would otherwise have built 100 miners’ cottages (reckoned at one two-roomed house with verandah for every 50 stoppings, 6J in. by 7 in. by 4J in. brick work), and as much timber for supports and fences, as would probably have kept the whole effective working portion of the mine going for roof supports. By the time the boundary is reached 20 per cent, of the coal resources in the mine will have