March 9, 1917. THE COLLIERY GUARDIAN. 483 appendix to the i eport issued in January last year,*and it is very carefully described there. A circuit was formed, consisting of a baittry, a post office resistance box, a trembler bell, and an explosion vessel. The post office resistance box was employed to vary the current passing in the circuit, its coils being wound so as not to give rise to any induction in the circuit; this is the usual arrangement with resistance coils employed for taking accurate measurements of small currents. The important part of the apparatus was the explosion vessel. It was a glass globe of 500 cu. cm. capacity, about 30 cu. in., and it carried a fixed contact near the centre of the globe, and a flexible moving contact that was brought into connection with the fixed contact every five seconds, the two being maintained in contact for about half a second, the connection being then suddenly broken. The moving contact consisted of a strip of metal bent at an angle so that the above scheme could be carried out, and attached to a rod which was revolved by the aid of an electric motor, and kept the moving contact revolving in the globe, meeting and leaving the fixed contact as often as the latter crossed its path. The arrangement for making and breaking connection between the two contacts appears to the writer to be very good, to have been very care- fully worked out, and to very fairly represent the make and break between naked signal wires; but the arrange- ment of the 500 cu. cm. globe from which the atmosphere was carefully excluded, and into which measured quantities of gas and air were carefully passed, does not at all represent the conditions on an engine plane between the signal wires when the signal is made. On all haulage rhads various Acts of Parliament have decreed that there shall be a powerful air current flowing, so that the conditions are quite different from those in the small glass globe employed by the ex- perimenters. The conditions they produced were necessary to enable them to vary the percentages of gas present where the break flash occurred, but they in no wise represented the actual conditions ruling. The view which the writer formed nearly 30 years ago was that the cases where an explosive mixture would be present on a haulage road at the moment when the signal was given would be extremely rare, and that even where an explosive mixture was present it would be exceedingly difficult to ignite it by the spark between the wires after a signal had been given. As those who were working at the shot firing problem 30 years ago discovered, and as motorists to-day know to their cost, it i s not at all an easy matter to ignite an explo- sive mixture with an electric spark. The writer feels that the Home Office experiments have done very good work by producing apparatus, such as the double-wound bells, which they recommend for signalling purposes ; but his feeling is that the danger from a spark between the signal wires was small before these experiments were carried out, and that if the double winding of the bells is generally adopted the danger is practically eliminated. The Trembler Bell and the Relay. But as the experiments show, the danger from trembler bells and relays, particularly from trembler bells, is very serious. The danger is so slight at the flash between bare wires, because it has not sufficient time to ignite the mixture; with the trembler bell, giving rise to a number of sparks, the case is quite different. There is time to heat the air in the neighbour- hood of the contact, particularly if it is enclosed in an iron case, and to ignite it. The succession of trembler' sparks do what the compression stroke in a gas engine does. Trembler' bells, too, are often fixed at parts of the road, and in positions where the atmosphere is more or less stagnant, so that it would have a greater chance of ignition. Mining men prefer the trembler bell to the single stroke for various reasons, mainly because they find it more sensitive and more certain. In view, however, of the danger of the spark at the trembler- bell, the writer suggests that the single-stroke bell should be given another chance combined with the relay; if both have double windings all danger from sparking should be completely suppressed. The experi- menters say that the trembler bell having its works enclosed in a gas-proof and flame-proof case should be safe. The writer would very much doubt this ; it is very difficult to make the case both gas-proof and flame- proof, and to ensure that it shall remain so after the bell has been working, its armature vibrating, and innumerable sparks passing for some time. The bell will be almost sure to require regulating at some time oi' other, and it will be difficult to ensure that the flame- proof condition will be reproduced ; the heat liberated bv the sparks also will probably cause breathing, as in ebctric motors, and an ingress of an explosive mixture if one is present. Managers’ and Under-managers’ Certificates. — An examination for first and second-class certificates of com- petency as manager and under-manager of mines will be held on May 22, at Edinburgh, Newcastle-upon-Tyne, Sheffield, Wigan, Cardiff, and Birmingham, under the Coal Mines Act, 1911. An examination for certificates of quali- fication as surveyor of mines will be held at the same places on May 23. Candidates, on or before April 7, must send their names and state the district in which they are employed, to the Secretary, at the Home Office, Whitehall, London, S.W., from whom all particulars can be obtained. THE WOOD CIRCULAR CAR DUMPER.* The Wood dumper is a device for dumping coal at the bottom of a shaft in order to increase the hoisting capa- city of mine cages, with the purpose in view of increas- ing the production capacity of deep shaft mines. It is nothing more than a rocking cradle device, which, by making a trifle more than a half-turn, allows the coal to roll gently out of the car upon a chute pitched at a gentle slope. This allows the coal to fall into a skip, which is placed immediately below. This skip has a capacity of eight tons, equivalent to the contents of two ordinary mine cars. So far, only two of these devices have been installed in the United States, but arrangements are being made for the installation of others. One of them is at the mine of the King Harlan Mining Company at Kildav, in Harlan County, Kentucky; the other at the mine of Bell and Zoller at Zeigler, Franklin County, Illinois. The former is on a slope opening. The latter is at the bottom of a shaft, something like 650 ft. deep, showing the influence therefore on deep shaft mining. The latter is the most interesting installation of the two. When Joseph Leiter was operating the Zeigler mine, he did not believe in hoisting the mine car to the sur- face, because he thought that that was unduly delaying the mine cars, which should be devoted to their original purpose, which was to haul coal to the shaft bottom. Also, he did not believe in slowing down the shaft, speed by using small cars on the cages. Instead, he sought to provide a system by which the mine cars should dump Trip of Cars ready to be Dumped. 3® .. ’ ■ their loads at the bottom of the shaft, and that these loads should be hoisted to the surface in a box or skip capable of carrying more than a single mine car. In consequence, he installed an entirely new system, which was to allow the cage carrying its skip to drop into the sump in the mine, and then to have the mine ear run over the top of it and dump its load in passing. To make this operation possible, he introduced dump bottom cars in his mine, and the Zeigler property was so operated for a number of years. The drop bottom car, however, had its disadvantages, which it seems impossible to avoid. For instance, the oars were subject to rather rough usage in the mines, and the bottoms would not always close tightly enough to retain all of the fine coal loaded in by the miner. As a natural result, coal dust was deposited all through the main haulage way, and in some places it became almost ankle deep. Each passing car stirred up the dust, and, of course, made that a dangerous mine, because any explosion of gas in the interior would find large quantities of dust which would support and feed a mine explosion; and the use of drop bottom cars there- fore was always considered dangerous in the Leiter mine, and it was something which the managers of Bell and Zoller wanted to get rid of when they took over that property. However, to change away from the Leiter system was not easy, because of the depth of the shaft, which was, as indicated, about 650 ft. To have run a line of cars direct upon the cage without increasing the speed of the hoist, or without, in fact, making over the entire mine, would have resulted only in a marked slowing down of the production, which, of course, was out of the ques- tion. The difficulty was, however, overcame by the installation of the circular dumper, introduced by Mr. A. H. Wood, which had been in operation successful!; for some time at Kildav, Kentucky. It being impossible to shut down the mine while the new dumper was being put into position, arrangements had to be made to instal the new device with a delay of no more than one day, and this was carried out during a holiday week. Since that time, it has been in con- stant operation, and, from present indications, will increase the production from about 3,500 tons a day to nearly 5,000 tons a day in very short order, and to 6,000 tons a day so soon as development work will make that possible. According to the new arrangement, the old plan of dropping the skip into the sump and loading it from above is retained, the new device merely replacing the platform over which the cars formerly ran to dump theii* cars. This new contrivance is in reality a cylinder with the stays in place, but without any side boards. The mine car is run upon a track, which is conveniently placed in * The Black Diamond. the cylinder, and is automatically clamped into place. This cylinder is large enough to hold two ordinary mine cars, each having a carrying capacity of four tons. As soon as the car is clamped in place, the attendant pulls a rope which works a pneumatic piston. This in turn revolves the cylinder, with its two cars of coal, a little more than a half-turn, and puts the cars in a posi- tion where they spill the coal slowly over the side, and drop it upon a plate or chute leading directly down to the skip beneath. Thus the two ears drop their loads upon this plate, filling the eight-ton skip underneath. When the cars have been emptied, another operation of .the piston returns the cylinder to its first position, and the empty cars, still coupled together, are bumped off by the two loads, which are then let down, and travel down a slight incline to the gathering yard. The speed of this mechanism is so timed that it can dump coal three times a minute, or, in other words, it can dump six cars of coal, or 24 tons, a minute. This implies, of course, that the skips containing eight tons of coal can make three trips up the 650 ft. shaft in a minute, which is now a common practice. . Figuring the theoretical capacity of a shaft so equipped, it is only necessary to assume an eight-hour working day and 24. tons of coal a minute to find that the productive capacity of the mine is better than 11,000 tons a day. This compares with the world’s record, established at Gillespie, Illinois, viz., 5,502 tons in one day of eight hours. This compares with the previous record of 5,285 tons, and with a record held for years of 5,195 tons. One of the most interesting things about this change is that it has allowed the management to get rid of the drop bottom cars which have been scattering dust along the mine haulage way and making the mine dangerous, as previously described. Another great advantage claimed is that it allows a solid pit car to be used, thus getting away from the practice of using a gate at one end of the car. It is believed that this will make the mine ears far more durable. Also it is claimed for this device that, although it involves two dumpings of the car instead of one, it actually limits the breakage, because arrangements are made for an easy flow of the coal into the skip, and a further easy flow from the skip direct to the screens. When the mine is equipped with this device, the weigh hopper on the tipple is done away with, and instead the ear is weighed in the mine on a scale placed just above the dumping platform. By weighing the loads and the empties, they get the net weight of the car, as is done above ground afterwards in connection with the railroad car. PRECAUTIONS AGAINST PIT ENGINE-HOUSE FIRES. The examination of the cause of an outbreak of fire in the engine-house at a Westphalian colliery, reported in Glilckauf, traced the fire to excessive friction in a new and ill-fitting' brake block. The burning splinters fell into the drum pit and ignited the shavings and greasy cleaning waste there, the flames spreading to the rope grease covering the bottom of the pit, and thence to an adjoining wooden stage and the woodwork on the drum. The winding rope burned through and the cages fell, but were arrested by the White and Grant safety-catch apparatus with which they were provided. Various proposals have been made to preclude the recurrence of similar dangers, including the provision of spraying devices, which, however, would entail constant supervision. Filling the drum pit with water is as little likely to be successful—in view of the low specific gravity of the grease, and the difficulty of keeping the water level constant— as covering the bottom of the drum pit with sand, which, whilst ensuring the absorption of oil, would not prevent the accumulation of greasy waste and shavings. Another proposal was to have a communicating passage between the drum pit and the outer air, through which any outbreak of fire could be directly attacked with extinguishers. This was also ruled out, because the door of such passage would have to be kept locked, and there would be delay in finding the key ; and, unless the door joints were kept perfectly tight, the passage would form a flue tending to spread the fire. None of these methods struck at the real root of the evil, namely, the practice of leaving shavings, waste, &c., in the drum pit. The simplest and most reliable way, therefore, is to see that such dangerous materials are cleaned out of the drum pit at regular intervals, say every 8 to 10 days, under proper supervision, and to replace all woodwork in the engine house by iron. The dates of cleaning should be entered in a book, with the result of the subsequent inspection. The responsible manager should inspect the condition of the drum pit, engine-house cellar, etc., at least once a quarter, and see that the appliances for fire extinction are in good order, entering his report in a book, so that the technical manager can always see that the work has been carried out with the requisite care and thoroughness. The Firth of Forth Coal Field.—At the monthly meeting of the Edinburgh Field Naturalists and Microscopical Society last week, Mr. J. J. M'Beath read a paper on “ The Origin, Local Distribution, and Working of Coal.” Referring to recent developments in coal working, the lecturer recalled a project of the late Mr. D. Landale, com- municated to the Edinburgh Geological Society in 1864, still waiting to be realised, for winning the immense deposits of the Firth of Forth coal field by means of shafts and tunnels from Inchkeith. Mr. Landale estimated that an expendi- ture of less than a quarter of a million pounds, reckoned in the values of those days, would provide for pits, tunnels, railways, miners’ cottages, and a landing place on the island, and place 135,000,000 tons within reach of the miner, a modest portion of the two and a half thousand million tons which the Royal- Commission in 1905 estimated to be available at depths less than 4,000 ft. in the under-sea area east of Inchkeith.