in use, and to consider the desirability of compelling sinkers to use a particular form. Two forms are in common use, the half-circle and the isosceles triangle, and the evidence tendered as to the relative strength of these was contradictory. The balance of evidence, however, was in favour of the triangular form. The halfcircle is subjected to a bending strain while the loaded bucket is being raised, its tendency being to straighten out. The results of tests made showed that with the same metal, the same section and the same load, the superiority in favour of the triangular form is as 15 to 11. These results are in agreement with practical experience. Trials with iron of different quality showed that ingot-iron is unsuitable for the purpose. Only the best wrought-iron should be used, and the bail must be in one piece, that is, without a weld. The most suitable section was found to be the oval, the extension of whose longer axis would be within the triangle. The ear-bolts should be calculated to carry, not one-half, but seven-tenths of the load, to meet all contingencies. Formulas for calculating the dimensions of bails are given, with illustrations. G. G. A. Drop-Shaft Sinking. C. T. RICE. (Engineering and Mining Journal, New York, 1913, pp. 509–511.) In an article on shaft-sinking at the Indiana Mine in the Michigan copper country, the Author describes the construction and sinking of a steel and concrete drop-shaft through an overburden of 100 feet of sandy material. The shaft-casing was made up of annular sections of steel-plate, the first 8 feet in diameter, gradually reduced as each ring was bolted inside the next preceding one, with an overlap of 4 inches. The two lower rings were of -inch plate, those above being of -inch iron. A g-inch by 6-inch angle was fastened to the bottom plate to stiffen the ring and give a stronger cutting-edge, as well as to facilitate concreting. The concrete was put in from the bottom upwards, collapsible wooden forms being used. The shaft-opening left within the lining was octagonal. The thickness of the concrete was calculated to give sufficient weight to overcome a frictional resistance of 400 lbs. per square foot. As this casing sank through the sand another ring was bolted on, the collapsible form moved up, and a new section concreted. Reinforcement with a few wire-ropes was resorted to only in the upper 10 or 12 feet of the completed shaft. When the solid rock was reached the material within this steel-and-concrete caisson was excavated. A smooth shelf was then cut in the rock by a hammer and drill, and the joint sealed with concrete. This portion of the work was accomplished in 3 months. The total cost averaged 30s. per foot. Illustrations are given. G. G. A. Underground Haulage at the Pit-Eye. (Glückauf, Essen, 1913, p. 379.) In underground haulage by locomotives the usual practice is to push the train of some fifty tubs forward, tub by tub, to the cageloading point at the pit-eye by means of a locomotive at the rear. In most cases a locomotive is kept constantly at work during the shift in this way. From an economical point of view this is unsatisfactory. The problem has been solved at one of the mines at Gelsenkirche in Germany. A short, single-line, endless-chain haulage-system has been constructed, from the point at which the incoming trains stop to the pit-eye. The electrically-driven chain, with its pulleys, runs below the tramway and takes the train of loaded tubs up to the pit-eye at the rate of 15 yards per minute. The empty tubs are run back to the locomotive-station, where they are again made up into trains by a similar endless-chain system. Only one man is required to detach the loaded tubs and to hook on the empty ones. The chief advantage of this system is that its working-cost is much less than that of the locomotive, only about one-fourth in the mine in question. The 7-HP. electro-motor may be installed either in a side-chamber, in a cross-cut, or below the tramway it is designed to work. The length of the haulage-line is about 100 yards. An illustration is given. G. G. A. Work of Underground Locomotives. A. BAIJOT. (Annales des Mines de Belgique, Brussels, 1913, vol. 18, pp. 3-30.) The work of underground locomotives is considered, and their efficiency and running-cost are approximately calculated. The Author deals with the petrol-locomotive commonly in use in the Belgian mines. But as compressed-air works out at about the same cost, the results of 2 years' experience here shown are applicable to locomotives of that class. The type of locomotive in common use is one of 12 HP., designed to run at a speed of 120 metres per minute with a full load on the level. It has been found in practice that, with such a motor, running under favourable conditions of load and line, 500 ton-kilometres in a 9-hour shift can rarely be exceeded. In most mines the work accomplished is less than 400 ton-kilometres. To reach this degree of efficiency heavy trains of thirty-two to forty-two tubs, carrying a total load of 30 tons, must be made up, and as little time as possible lost in shunting or through delay. Tubs with "loose" wheels are derailed more often than tubs with wheels fixed to the axles like railwaytrucks. Economy requires that the locomotive should work up to nearly its maximum power, and the rails be well and firmly laid. Experience in the Belgian mines shows a haulage-cost per shift of 5 to 7 centimes per ton for 400 ton-kilometres, 8 to 11 centimes for 250 ton-kilometres, and 13 to 20 centimes for only 150 ton-kilometres. These figures show that when working under average conditions, locomotive-haulage is cheap. Also, in comparison with horse-haulage, a much larger tonnage may be dealt with for a given distance and time. Moreover the plant suffers less in wear and tear. An objection to the use underground of the petrol-motor is the smell of the combustible. The Author asserts, however, that when there is only one locomotive to every 5 cubic metres of air passing per second the smell is not offensive. When a locomotive is derailed, a better method of replacing it than with jacks and levers is to lay down round mine-timbers, and then, with another locomotive, pull the derailed one back on to the line. G. G. A. Conditions of Safety for Safety-Lamps. E. LEMAIRE. (Annales des Mines de Belgique, Brussels, 1913, vol. 18, pp. 47-79.) When gas is ignited inside a safety-lamp the gauze is quickly heated to redness (1,000° C.), at which temperature the flame passes through and may ignite gas outside the lamp. Obviously the degree of safety afforded by a lamp is dependent on this heating of the gauze. The results of a very complete series of experiments made at the Government testing-station at Frameries are given in this article. The dangerous temperature (of the gauze) lies between 700° and 1,000° C. The larger the volume of gas within the lamp the more quickly is the gauze heated up to that temperature. Therefore, other things being equal, the smaller the diameter the safer the lamp. The authorized dimensions for a safety-lamp in Belgium are: for the outer gauze 42 millimetres at the top and 49 millimetres at the base. The degree of heating depends further on the quantity of gas entering in a given time. For a given lamp, this depends on the velocity of the air-current carrying the gas. The stronger the current the less safe is the lamp. For a given current the quantity of gas entering depends on the resistance offered by the gauze. Therefore, the smaller the mesh the safer the lamp. For this reason an old lamp is in a marked degree safer than a new one, for the wires of the latter have become oxidized and the mesh made thereby smaller. A shield also notably hinders the entrance of gas. A benzine lamp is less safe in a current of air than a vegetable-oil lamp. Theoretically a gauze should allow an igniting flame to pass at a temperature of 650° C. In practice, however, it is found that a higher temperature (at least 700°) must be reached. The higher the percentage of gas in the air the higher may be the temperature of the gauze. Generally a double gauze offers greater safety than a single gauze. The conditions and results of this long series of tests are appended to the article in tabular form. G. G. A. Edison Electric Safety-Lamp. (Electrical World, New York, 1913, vol. 61, p. 177.) A description, with photographs, is given of the miner's electric safety-lamp for which Mr. Thomas A. Edison was awarded the Rathenau gold medal in 1913 by the American Museum of Safety. Two nickel-iron cells are used giving 4 ampere-hours with an electromotive force of 2.4 volts. The battery complete weighs about 2 lbs. and is 5 inches wide and 4.5 inches high. Spring terminals on the battery connect with nickelled-steel contact-plates fixed to, but insulated from, the top of the case. When the hinged top is brought down and fastened the battery is secured and the case may be locked. The twin-conductor flexible cord is provided at one end with a terminal, which, when pushed into a socket on the top of the battery-case, becomes fastened in such a manner that it cannot be disconnected without unlocking the case. The lamp is a tungsten one rated at 2 candle-power, and is carried on the front of the miner's cap enclosed in a sealed case containing a parabolic reflector and a thick glass lens. The twin-conductor is carried over the cap in flexible steel, through a loop at the back and down to the battery-case hung on a waist-strap behind the wearer. P. T. S. Fleuss Life-Saving Apparatus. J. TAFFAREL. (Annales des Mines, Paris, 1913, vol. 3, pp. 83-110.) The several types of breathing-apparatus in use in coal-mines have been severely tested at the Liévin testing-station for investigating the causes of fire-damp and coal-dust explosions, and the Author, who is the manager of that station, has found the Fleuss apparatus to be the most satisfactory. This is an English invention some 35 years old, but recently improved in design and construction in accordance with later experience. It consists essentially of the usual four parts: (1) a bottle of oxygen of 1 litre capacity, compressed to 120 atmospheres, giving a constant supply of 2 litres per minute for about 2 hours; (2) a reducing-valve to control the discharge of the oxygen; (3) a regenerator, consisting of a rubber bag divided into two compartments and containing sticks of caustic soda, which bag is connected by flexible tubes with the mouth of the wearer; and (4) a cooler, a metal box surrounded by a covering of asbestos saturated with a mixture, in equal parts, of water and methyl spirit. The air exhaled passes through the box before entering the regenerator. The Author, after subjecting it to severe and prolonged tests, found this apparatus very reliable, and he recommends it for its simplicity and certainty of action. Once set in action, the wearer has only to assure himself from time to time, by a glance at the pressure-gauge, that he has sufficient oxygen in reserve. Its weight-about 37 lbs.-which is less than that of the Dräger, may be reduced to 27 lbs. by using an oxygen bottle similar to that of the Tissot apparatus. The parts being strapped to the back and the breast, the shoulders are unencumbered. The proportion of carbon-dioxide never exceeds 1 per cent. in the regenerated air. The proportion of oxygen must not fall below 21 per cent., which is that of the atmosphere. It may, however, exceed that amount in any degree without bad physiological effects. The proportion given by this apparatus is 80 to 90 per cent. The working-cost is less than that of any other system. Illustrations are given. G. G. A. Electrode-Connections in Electric Furnaces. (Stahl und Eisen, Düsseldorf, 1913, pp. 472-478.) The question of a sufficient and suitable connection between the conductors and the carbon-electrodes in an electric furnace is one of primary importance; for the efficiency of the furnace and the working-cost are largely dependent on that connection. At works, the annual output of which amounted to 4,000 tons of ferro-alloys, the cost of connections was, by improved forms, reduced from 68. 5d. to 18. 7d. per ton of metal produced, while at the same time the consumption of the material of the electrodes was notably lessened. The problem for the designer, which has not yet received a wholly satisfactory solution, is to use as much as possible of the electrode without injury to the connections. Whatever the form of the contact, it should cover as large a surface of the electrode as the conditions of the case allow, and that surface must be hard, smooth, and free from dust. To give some degree of elasticity to the connections it is usual to place thin copper or iron plates between the carbon and the clamp. When the surface is rough or irregular in shape a pad of fine copper-wire is sometimes inserted between the carbon and the copper plate to ensure good and even contact. the production of carbides the permanent connection is made with the end of the electrode, which is variously shaped for that purpose. But in the electro-steel furnace, the carbon electrode is clamped at any portion of its length to the conductors, thus providing a shifting contact. To lessen the waste in carbon "ends," it is necessary to burn the electrode up as close to the final contact-point as possible. To do this a system of water-cooling has been applied to the connections with satisfactory results. The Author describes and illustrates this system and all forms of connection now in com mon use. G. G. A. For |