80 THE COLLIERY GUARDIAN. July 10, 1914. thereby ensuring identical pressure inside and outside the chamber at the instant of reading—a condition that cannot be guaranteed with a sealed single-chamber instrument, owing to causes already fully described. The same device, when fitted to one of the many auxiliary fresh-air renewal reservoirs made by the author, gave a supply of pure air at atmospheric pressure for several readings, after which the reservoir had drawn in sufficient external atmosphere to render the purity of its contents uncertain. This instrument can be used for small quantities of gas, but must either be discarded or exposed for five minutes to known fresh air after gas has once been found by it. Absorption Instruments.—It is to this class of instru- ment that the writer turned finally in search of a safe and reliable means of detecting methane in a practical manner by both hewers and firemen, and, with the assistance of Mr. A. E. Mundy, he has evolved seven or eight patterns, which, while all detecting the presence of small quantities of methane, have their several advantages. The primary principle of all these instruments is the absorption of methane (CH4) by a catalytic material called “ methanium,” contained in a hermetically-sealed chamber. A U-tube is employed and a pair of balancing chambers, as shown in fig. 3, so as to eliminate tempera- ture and pressure effects. The next important matter is to secure the inclusion of a uniform and sufficient quan- tity of the gas that is being tested, and this is effected by the various methods stated below. SECTIONAL ELEVATION fig.h. Sectional elevation Fl GUI fig.ii. SECTIONAL ELEVATION SECTIONAL PLAN SECTIONAL ELEVATION SECTION OH AA The simplest means is the use of a double-chamber diffusion instrument (fig. 3), with the absorbent in one chamber only, both being balanced for cubic capacity, but unsealed simultaneously (fig. 4). Even with a very dense medium, however, the period required for an indi- cation and the dynamic losses due to the diffusing-out as well as the diffusing-in proved appreciable. Another method is to place the catalyst above one of the chambers and rotate both chambers away from the apertures for the U-tube and the catalyst recesses, take a sample of the air to be tested by waving about, or holding in the air-current, and then turn the chamber back into connection with the tube and catalyst, when absorption will take place. The instrument can be arranged either in tap form, provided with holes in the plug as the collection-cham- bers, or with super-imposed cylinders rotating on the same axis with or without diffusion media (figs. 5 and 6). The writer has found, however, after making up dozens of patterns, and testing them all exhaustively, that the most satisfactory, from both the manufacturing and from the economic points of view, is an instrument on the lines of fig. 7, which is a combination of the diffusion and absorption principles. In this detector porous media are used at the opening of the balancing chambers. These media are fitted loosely, so as to allow the air to escape while the methane is drawn in by osmosis : the gas being thus enclosed, with no pressure created by diffusion, temperature, or humidity, and no valves to jeopardise the accuracy of the readings. After a given period for the inclusion of the suspected atmosphere, both chambers are simultaneously closed hermetically by rotating the cover of the apparatus, when, if gas be present, absorption will occur. This design also facili- tates the renewal operation in the lamp-cabin, which consists merely of tipping out the old methanium and media and dropping in a fresh supply, the cost being but a fraction of a penny. The absorbent material is the result of much research by Mr. A. E. Mundy, who believes that he has in the course of his investigation discovered a new alloy or compound. This instrument, costing less than a shilling, attachable to any electric lamp, or entirely complete in itself (involving no hot wires), has been tested in 1| per cent, of gas against a fireman’s lamp in a Yorkshire pit, and gave differential indications of three-quarters of an inch. If a number of instruments are used for one reading only, that reading can be retained for the subsequent inspection of the surveyor at the pit-bank. After a reading has been taken in gas, the instrument is opened up; if gas is still present, a second indication occurs, when the instrument is closed again, and such reading will be in ratio to the percentage of methape in the surrounding atmosphere. The principle is equally applicable to the detection of carbon dioxide, and the writer hopes to develop the instrument for that purpose, with the view of perfecting it to such an extent that it can be used with confidence in the place of flame-indicators, and thus entirely delete the final element, of risk from illumination or gas-testing in mines. The apparatus exhibited by the writer is for the pur- pose of demonstrating the principles involved in this important problem. In deciding upon the form of detec- tor which mining engineers propose to use in the place of the flame lamp, the following conditions must be taken into account, the apparatus exhibited and the figures in the text illustrating some of the difficulties encountered in endeavouring to perfect a mine-gas indicator. The unstable atmospheric conditions in the mine are :— Varying Temperature.—Due to depth from the sur- face, velocity, temperature, and volume of the ventilat- FIG v test position SECTIONAL ELEVATION fig. si. TEST POSITION SECTIONAL ELEVATION SEALED POSITION TEST POSITION 2LAN ing current, radiation to walls, floor, and roof, radiations from animal bodies and mechanism, and evaporation and condensation of moisture. Pressure.—Due to depth from the surface and the conditions of ventilation and the barometer. Humidity.—Due to the condition of the mine and of the indrawn current of air, animal life, etc. Dustiness.—Due to most of the aboue general con- ditions. Velocity and Direction.—Due to ventilating conditions. Fig. 1 depicts a single-chamber diffusion instrument with U-tube attached, with which the writer has carried out many experiments, and for the purposes of the meeting it is provided with a sliding cover, so that the chamber can be opened by simple rotation of the cpver. The first experiment is to close the instrument in air and immerse it in an atmosphere containing pit-gas from Cymmer Colliery, South Wales, the mixture being at the same temperature and pressure as the room. A rise of the index in the U-tube will be noted, due to the inward diffusion of the pit gas faster than the residual air can pass out. As the instrument remains in the mix- ture, the index rises to a maximum, and then falls to zero. When the device is removed from the bell-jar, a reverse reading will be noted, due to the gas rushing out faster than the air can pass in. On the instrument being again filled with air and the experiment being repeated, the same result occurs. If, however, the apparatus is taken from the first jar, and immersed in a second jar with a weaker mixture of methane and air, a feebler movement is noted. Again, if the instrument be filled with air and im- mersed in the second weaker mixture, the results are entirely different from those when the instrument is taken from the strong mixture into the weaker. Thus, unless the density of the internal atmosphere is known, the results are totally unreliable. The second experiment illustrates the effect of varying temperatures on a single-chamber diffusion-instrument. The closed detector full of air is inserted into the bell-jar containing air only, but 10 degs. higher than the tem- perature of the room. An excellent reading on the right is observed, but with no gas present. If the instrument be now closed in the hot air, and brought into the cooler air of the room, a reverse reading is obtained. If the closed instrument is held in or against the hand, a heat reading ocurs—all with no gas present. If a mixture of carbon dioxide and air at the same den- sity as air is present outside the chamber, with an inside chamber, no effect is obtained. The internal at- mosphere of this single chamber cannot be standardised by breathing on the instrument, as the breath varies in its constitutents, temperature and also combines with the mine air to such an extent as to falsify the indi- cations. It is obviously impracticable to bring the instrument out into non-gassy air between each reading, even if the air could be renewed with certainty at a uniform temperature. From the foregoing remarks it will be obvious that, unless compensation for heat and pressure effects is made by some method unknown to the writer, it is physically impossible to make an infallible diffusion or absorption instrument with only one chamber, or one leg of a U-tube. Fig. 3 illustrates a diffusion-instrument with two opposing chambers, the essential parts of which have been patented in Germany, the United States of America, France, Great Britain, etc. When this instru- ment is passed through the same tests as the single- chamber instrument, it will be noted that it is sensitive only to gas and not to temperature also. Fig. 6 shows a double-chamber instrument in the form of a tap, holes in the plug of the tap forming the FIG3ZH M - METHANE 4 MOISTURE M1 - MOISTURE 011LX SECTIONAL ELEVATION SECTION Ct-; „ TEST POSITION SECTIONAL ELEVATION ADMITTING POSITION SECTIONAL ELEVATION PLAN collection-chambers with the U-tube below and the absorbent above. When the tap plug is in one posi- tion, the mine air blows through freely; but all the other chambers are short-circuited, in order to equalise all the pressures and restore the index to zero. On the plug of the tap being turned round, the holes are brought into line with the U-tube, and the catalyst as also any gas in the chambers on the left hand side is absorbed, there- by drawing up the index. Fig. 5 is a larger instrument (partly described earlier in this paper), with detachable plugs, A1 and A2, for refilling with methanium, and will detect very small per- centages of methane. Its operation is as follows :—The middle portion B is rotated around the centre pin until the holes TT are opposite the holes in the top cases and the base, simultaneously opening the ends of the U-tube and admitting the suspected atmosphere to TT at normal temperature and pressure. After about 15 seconds’ ex- posure to the atmosphere, section B is turned back again, in line with the U-tube and catalyst, permitting absorption of any gas in the chamber T1. The following experiment demonstates inaccuracies that result with single-chamber instruments when they are used, in varying temperatures, such variation being caused either during barometer changes or when ascend- ing or descending from one mine-level to another.