July 10, 1914. THE COLLIERY GUARDIAN. hoppers together, at right angles to the rail track in line with the ovens. Such an arrangement, however, neces- sitated the removal of the gas collecting main from its usual place, the centre of the ovens, to one side. The collecting main thus takes the place which is otherwise occupied by the rails for the door lifting winch, but, in some plants the collecting main is supported so high from the ovens that the door lifting crane can pass under- neath, or the main rests near the top of the ovens, and projects over the machine side doors. In this case other means must be adopted for the removal of the doors, generally by an arrangement in connection with the pushing machine. The girder work of the collecting main generally carries the overhead wires for the current supply to the car. Fig. 3 shows the charging car of the Koppers Coke Oven and By-Products Company, of Sheffield, which consists of three hoppers resting on a girder frame which is carried by two axles with four travelling wheels. The sides of the middle hopper are set at the same angle all round, while the outer side of the two-end hoppers are vertical. The girder frame is extended on one end of the machine as a platform, and holds the driver’s cabin. In the cabin the switch, controller, foot brake and the three levers for operating the slides are placed, while the motor rests on one side on the girder frame. The motor, which is totally enclosed, is of 20-horse power, and drives one of the travelling shafts, and gives the car a speed of 60-100 m. per minute. Between the driver’s cabin and the three hoppers a gangway, accessible by steps, is placed right along the three hoppers. The whole machine rests on roller bearings; it holds nine tons of coal, and all rivets and bolts inside the hoppers are countersunk so as to prevent the coal from sticking to any unnecessary projecting parts. A car of similar design to the above serves a coke oven plant of 120 ovens in Westphalia, and charges over 50 ovens per 12 hours shift. Fig; 4 shows the charging car made by F. M6guin and Company, Dillingen-on-Saar, Germany, for the coke oven plant of the Glamorgan Coal Company Limited. The three hoppers are equal in size and capacity in this machine, every hopper has one vertical and three inclined sides. The girder frame of this machine rests in roller bearings on one shaft, which is driven by gear wheels from a motor, which is also fixed to the counter shaft. The other two wheels have short shafts just long enough to receive a bearing on each side of the travelling wheel. The girder frame rests by means of wagon springs on An Instrument for the Detection of Firedamp in Mines. By F. J. TURQUAND. Paper read at the meeting of the South Staffordshire and Warwickshire Institute of Mining Engineers. The writer is conscious that most members of this institute have had many years’ more experience with coal gases under natural condition in coal mines than he can lay claim to. The electrical or chemical problem of detecting the presence of dangerous gases, is, how- ever, distinct from the engineering problem of regulating and removing the same when they are unwelcome intruders, and the question of identifying and indicating pit gases is one to which the writer has given special attention for some years, with results that may interest mining engineers from a practical point of view. His paper deals solely with the commonest deleterious gases, namely : firedamp and carbonic-acid gas. Both these gases are readily detected by means of the safety oil-lamp to a more or less accurate extent, the dangers common to such oil-lamps being, of course, always pre- sent. The physical characteristics of the gases brought into use are the inflammability of the methane in the one, and the non-support of combustion by the carbonic acid in the other. Besides the flame method of detecting these gases, other methods have been used, which may be classified as follows :—(1) Thermometer instruments, (2) hot-wire instruments, (3) diffusion instruments, and (4) absorp- tion instruments. Thermometer Instruments.—The Sussmann Electric Miners’ Lamp Company Limited, some years ago made an instrument (and attached it to their lamp) consisting of a thermometer, the bulb of which was imbedded in spongy platinum or palladium. In the presence of methane a temperature rise was obtained with quite a small percentage. The causes of inaccuracy, however, were the varying temperature and humidity of the mine atmosphere, also the difficulties of standardising the catalyst and of preventing degeneration from dust particles. Heated Platinum and Palladium Wires.—When in the presence of methane, these wires undergo changes in length, colour, temperature, and electrical resistance, and will also burn out the charge by slow combustion. Hot-wire instruments are those in which the above into the chamber, and balances the internal and external pressure, when the manometer index will stand at zero. The serious defects of this type of apparatus (illus- trated in fig. 1) are sensitiveness to changes of tempera- ture and pressure, deposits of moisture and dust, and the difficulty of renewing the standard internal atmosphere at atmospheric pressure. These defects will be referred to again later. Owing to the sensitiveness, simplicity, and safety of this method, the writer has spent some years in experi- menting with this class of apparatus, and, in conjunc- tion with Mr. H. G. Prested, in 1902 evolved a very sensitive instrument. It was discovered that within certain limits the smaller the diffusion area was in rela- tion to the chamber, the greater was the pressure obtained, and that by making up an instrument from a porous pot, and waxing nearly the whole of its surface and sealing it with a flexible diaphragm, excellent read- ings were obtained. The difficulties were, however, the apparent impossibility of a reliable flexible diaphragm possessing sensitiveness to fractions of a degree of tem- perature and pressure, unreliability in damp and cold atmospheres, and, finally, the necessity for fresh-air renewals (essentially at normal temperatures and pres- sures) between each test. The writer some years after- wards, in connection with Mr. W. E. Gray, designed and patented a device overcoming all these difficulties, except that of fresh-air renewals. The temperature and pressure errors were corrected by employing a U-tube with a liquid index, but with two diffusion-chambers (exactly similar in every respect), one on each limb of the tube. Heating or cooling then affected both cham- bers equally, the pressure on the index being equal at both ends. The instrument, with both chambers and media sealed from the atmosphere, was then immersed in the sus- pected atmosphere, and one medium only exposed at a time; but two successive readings could be taken, there being obviously two supplies of fresh air. The light or heavy gas diffused through, and a proportionate reading was obtained, due to the difference of pressure between dkla. .JiSa. J iHiHlI Fig. 5. these shafts. To enable the driver to see always in front of him, whichever way he may travel, the driver’s car is placed higher up in this machine as compared with the one in fig. 3, and is placed between the bench side and the middle hopper. The cabin only contains switch, controller and foot brake. Right along the hoppers on each side a bridge is placed, and opposite each hopper a lever is placed to manipulate the bottom slides. The latter are made in two halves, and geared on top. By pulling the lever they open in opposite direction with a minimum of friction, and are thus very easily manipu- lated. All corners inside the hoppers are rounded off by bent plates so that the coal will not stick to the corners, and is easily discharged. The hopper mouth pieces are made of cast iron which does not warp by the heat from the charging holes. Fig. 5 shows the charging car of the Schalker Eisenhiitte, Gelsenkirchen in Germany. These engineers have been anxious to avoid all corners in the machine hoppers, and have given them a circular and the outer hoppers a semi-circular shape. The hoppers are either riveted together with countersunk rivets or the seams are welded. Great stress has been laid upon the fact of the necessity of enabling the man in charge to see his track right in front of the machine. While on the previous machine the driver stands in the middle in his cabin, the present car is provided with two cabins, one between each hopper. One cabin is placed on the outer side of the bridge round the hoppers on one side, and the other cabin in the opposite direction on the other bridge. Each cabin is provided with separate controller and foot brake. The driver handling the controller stands, on the machines, always on the very end of the bridge, and thus can see the rail track immediately in front of him. He always uses the cabin nearest the edge of the machine pointing in the direction in which he is travel- ling, thus reducing the chance of accidents to a minimum. (To be continued.) characteristics are turned to practical account in the following manner :— (1) By noting a certain difference in colour between one heated wire immersed in air and another in a mix- ture of air and methane. (2) By noting the difference in electrical resistance and/or length of a heated catalytic wire immersed in an air-and-methane mixture. (3) By noting the difference in temperature and/or volume between two variable chambers containing hot platinum wires, one filled with air and the other with the suspected atmosphere. (4) By noting the difference of volume between two variable chambers, both containing test air, but heated with a catalytic and a non-catalytic wire respectively. The writer’s objection to this class of instrument is the existence of a certain element of risk in the employ- ment of warm or hot wires, the additional electrical connection involved, errors due to falling voltage, vary- ing velocity and temperature of the mine atmosphere, and the progressive deterioration of the catalytic wire. Diffusion Instruments.—Ansell designed an instru- ment depending for its action upon the varying rates of diffusion of gases at different densities through a porous medium into an enclosed chamber, and this apparatus, when used under standard constant labora- tory conditions, is very sensitive and accurate. The instrument is virtually a chamber containing or connected to a manometer for indicating changes of internal pressure with one wall or side of a porous material, such as porcelain, marble, terra-cotta, plaster, etc., and can be used for gases which are both heavier and lighter than air. Thus, if the chamber contains air and is immersed in a denser atmosphere, the rate of egress of the air will be greater than the ingress of such atmosphere, resulting in a decrease of pressure inter- nally, which decrease progresses to a maximum regulated by the porosity of the medium and the relative density of the gases. The heavy gas eventually finds its way the two chambers. Several methods of air-renewals with reservoirs were patented, but it was found impos- sible to make a fresh-air reservoir that would retain air at changing atmospheric pressures and temperatures, even with the lightest of valves, and any system of air under pressure proved impossible also. Further, even if the diffusion instrument itself were made insensitive to the above factors, an additional instrument would be required to indicate atmospheric pressure, temperature, and humidity, the rate of diffusion varying with each condition. An ex-colliery manager recently assured the writer that, generally speaking, the temperature of mine air never varied from one year to another. Possibly, there- fore, the author may have experienced the exception rather than the rule during his tests. If the assertion of the ex-colliery manager was correct, and temperature effects could be entirely disregarded, a useful little diffusion instrument, designed and pro- tected by the author some time ago, would be of con- siderable interest to the members, as it indicated both methane and carbon dioxide. The instrument is illus- trated in fig. 2 and is constructed as follows :— A single-chamber diffusion-instrument, fig. 1, is employed, and is fitted with a rotating cover or top, and an additional U-tube. The additional U-tube has a bore so fine that it takes days for the external atmosphere to penetrate its entire length, unless a considerable drop in temperature takes place. This tube carries no liquid, and is simultaneously sealed when the porous medium is uncovered. The top cover may occupy the following positions :— (1) When the porous medium is sealed from the outer air, and the dry tube open. (2) When the medium is exposed to the air, the end of the dry tube being closed by the same operation. The effect of adding the dry long fine-bore tube is to allow slight internal expansion and contraction to com- pensate for local temperature and pressure changes, and