THE COLLIERY GUARDIAN ' . AND JOURNAL OF THE COAL AND IRON TRADES. ______________________________________ Vol. CXI. ____________________________________________________________________________________ Firedamp Detector for Miners’ Electric Safety Lamps. Since the publication of the experiments on this sub- ject ■(Colliery Guardian, January 28, 1916), a firm of miner’s safety lamp manufacturers and experts have • carried out for me, in their laboratory, a series of experi- ments with platinum wires of small diameter, in contact with coal gas and also with firedamp from the mine. The results of these experiments are very striking. It will be noted that the coal gas becomes ignited when the platinum wire becomes raised to incandescence by the catalytic action of the gas, but in no case have I had an ignition of a mixture of firedamp and air, though I used wire of No. 40 gauge, J in. in length. The catalytic action takes place at a lower temperature in coal gas (probably owing to the presence of so much free hydrogen) than in firedamp (methane). The minimum current (2-volt cell) in coal gas is 0-29 ampere when in. length of 0-0015 in. diameter platinum wire is used. The variation in the current passing and the drop in voltage is not so great as in methane. Indeed, there is a very striking difference. In the case of methane, with the same wire, the minimum current necessary is 0-505 ampere at 1-95 volts. The drop was momentarily to 0-42 ampere, after which the amperage remained steady at 0-475 ampere. It will be seen, in the experiment dealing with this, that 0-4 ampere would be passing at 1-25 volts, so the effect of the methane on the wire was to drop the voltage momentarily by about one-third—a very striking result. Assuming that a wire was . connected in series with a 2-volt lamp, and the voltage was 2, the lamp would be giving 1 candle-power-. If the voltage dropped one-third, the candle-power of the filament lamp would drop momentarily to about one-fifth. Now, a sudden drop in the light from 1 candle-power to one-fifth could not fail to be noticed by a man using an electric lamp. I propose to fit the device with a glass so that the wire also .can be examined. By this means an approximate estimate of the percentage of gas present can be formed’ from the redness of the wire, as it is well known that the wire is brought to a varying. temperature by varying percentages of gas and air, and that the differences are distinctly visible to the eye. The experiment with methane shows what would represent the voltage of a 2-volt mining lamp cell approaching end of discharge. The cell would be at a voltage of about 2-2 at commencement of discharge, and about 1-95 after 10 hours or so. With regard to the effect on the platinum wire, this becomes incandesced in gas and then drops in tempera- ture to a bright red heat; or it may fuse if a high percentage of gas is present. Of course, the effect varies with the percentage of gas. One important point to which particular ■ attention should . be directed is the probability that, with a platinum wire in series.. with the .filament lamp, the: drop in'voltage across the lamp (in firedamp) would be so great as to bring the'filament in the lamp to a temperature below the ignition point of firedamp, so that if the filament became exposed owing to damage it would not ignite gas. This indicates the possibility of making a perfect safety lamp, one that would not ignite firedamp in any circumstances. It may be pointed out that the arrangement can be worked very efficiently with a 4-volt cell, that’is to say With the lamp and platinum wire in series. Using fin. of 0’0023 in. diameter platinum wire, the voltage across the filament lamp (a 2 volt 0’9 ampere Osram lamp) the voltage is reduced to about one-half. Using T3K in. of 0’0015 in. diameter platinum wire, the voltage is also reduced to about one-half, i.e., to about 1’1 volts. In the absence of a 1’25 volt filament lamp, that will give light for the time required of a miner’s head lamp, it is necessary to run the platinum wire in parallel with a FRIDAY, APRIL 28, 1916. By T. J. THOMAS. 2 volt lamp, and to provide, a suitable cut-out to operate in firedamp. Possibly a filament lamp may be made so that the platinum wire and lamp may be run in series, this being the most desirable method for obvious reasons. The wires used in the tests were carefully gauged with a micrometer, and the sizes are given. below. The analysis of the firedamp from the mine from which the gas for the experimehts was taken has been found to show that there , is no special peculiarity in its com- position as compared with that of other mines. . Fig. 1 shows how voltage is taken across cell, and current consumption (amperes) by platinum wire. Fig. 2 shows how voltage is taken across cell, and current consumption taken (in amperes) for either the lamp or platinum wire, or for both when in parallel, on the cell. Both sketches show arrangement of switches, resistances, etc. ' ' Experiments with Wires Only. On a test on the Thomas gas detecting apparatus the following, results were obtained Condition. Appearance^oLplatinum A Volts. llldJXldlu. All resistance in ____Moderate red ....... 0*475 ... 2’1 One cut out.................. Slightly brighter red 0*49 ... 2*1 Two „ ... ... „ }> 9i 0*50 ... 2*1 All resistance cut out Fairly bright red ... 0’505 .,. *2 1 In these tests the ammeter , was inserted between the resistance and the platinum filament and the lamp was Ammeter Diagram I Switch Switch Voltmeter Platinum Wire .Switch \ ■ / Lamp'®' £ in. The voltage lines were across the lamp. The resist- ance and platinum wire, were in series, and they were both together in parallel with the lamp. A 50 ampere hour capacity'2 volt accumulator used for test in ail these and following.cases, so that there was no drop due to; poor capacity of the cell. The platinum wire in above tests was 0-0015 in. diameter, and fin. length used for test. The lamp used at 2’1 volts took 0’90 amperes. The total current used would therefore vary from 1’375 amperes to 1*405 amperes, depending on whether all resistance was in -or cut out.. Condition. Appearafin1Xi??atinUm Amps. Volts. All resistance in ... Just red ............ 0’82 ... 2’1 One cut out................. Moderate red __....... 0*88 ... 2’1 ' Two ,, ......... Fairly bright red.... 0 91 ... 2*1 All resistance cut out „ ,, ......0’93 ... 2’1 In these tests the ammeter was inserted as before, and ’ the voltage is still across the lamp. The platinum wire is 0’0023 in. diameter, and f in. used.1 The total current now for both lamp and platinum wire varies from 1’72 amperes to 1’83 amperes, according as all resistance is in or cut out. No. 2887. - Condition. Appearance of platinum Amps. Volts. All resistance in ........ Dull red ....................... 1*25 ... 2*1... One cut out......... Fairly bright red......... 1*45 ... 2*1 Two cut out ....... Bright red........... 1*6 ... 2’1 All resistance cut out Good bright red __....... 1’7 ... 2*1 . In these tests the ammeter was inserted as before, and the voltage is still across the lamp. The platinum wire is 0-0034 in. diameter, and was fin. long. The total current now for both lamp and platinum wire varies from 2-15 to 2-6, according as all resistance is in or cut out. Condition. Appearanceof platinum Am Voltg filament. • All resistance in __.... No redness........... 2*05 ... 1*95 One cut out........ ,, ,, ___________ 3*15 ... 1’95 Two ,, .... ,, ,, ........ 3*85 ... 1*95 AH resistance cut out Just barely visibly red 4*35 ... 1*95 In these tests the ammeter and voltmeter were both as before. The platinum wire is 0-0052 in. diameter, and was f in. long. The total c.urrent for both lamp and platinum wire varies from 2-95 to 5-25, according as all resistance is in or cut out. A few other tests were made, using a 10 ampere hour capacity (continuous current) 4-volt cell, and putting lamp and platinum wire in series, but cutting out all resistance... Using f in. of 0-0015 diameter platinum wire, the wire and lamp just showed red, there would be therefore no light from the lamp. Using fin. of 0-0023 in. diameter platinum wire the lamp burns brightly, and the platinum wire glows good bright red. Volts across the lamp 2-2 amperes in circuit = 0-95. With f in. of 0*0034 in. diameter platinum wire the lamp • burned very brightly. Volts across lamp ,2’8. Amperes in Switch .Switch Cell Voltmeter Diagram 2 Platinum Wire (/> I circuit 0’81, but platinum wire riot red at all. With lamp and f in. of 0’0053 in. diameter platinum wire in series, and all resistance cut but, and using a 2-volt 50 ampere hour capacity cell, the amperes in circuit = 0’08, and the volts across lamp = 0-60. Lamp merely glowed while the wire was not red at all. Using the cell and fin. length of 0-0015 in. diameter platinum wire, both lamp and wire in series, and all resistance cut out, volts across lamp = 0-65, and amperes in circuit = 0-55; lamp just glowing, platinum filament red. Gauges of Platinum Wires Used in these Experiments. The wires were gauged very carefully with a micro- meter, and the correct sizes found to be :— 0’0015 in. dia. and area = 0’000002011. Approx, gauge 48 0*0023 in. „ „ = 0*000004524. ,, 3 46 0*0034 in. „ „ = 0*000009111. „ „ 431 0*0052 in. „ „ = 0*00002124. „ „ 39 Experiments with Coal Gas. (1) Using a 2 volt 50 ampere hour capacity (con- tinuous) cell, and placing lamp and platinum filament 0-0023 in. diameter in series with 3 yds. of No. 29 S.W.G. steel wire in parallel with the platinum filament