330 _____________________________________________________________ February 16, 1917. THE COLLIERY GUARDIAN. ____________________________ Replying on the discussion, Mr. Tate said there was no doubt that a Clwnny lamp gave 'a much better light for all ordinary purposes, but. under certain conditions, for officials travelling, a tin-can Davy was a very useful lamp, and its use ought not to. be prohibited. He thought that most members had been in positions in which they would have preferred to have a Davy lamp rather than run the risk of losing their light. If a man with a Clanny lamp came unexpectedly across gas, he would very often lose his light, where, with a tin-can Davy, he would retain his light, and there would be no fear. If the gauze of a lamp grew hot, nothing would take place unless it got very hot indeed, and there was a current. It would take no harm in the absence of a current. That was repeatedly proved in the early days, as he had shown in his paper. Dr. Louis had men- tioned Mr. Blackett’s contrivance for screening the light. That contrivance, however, was not a direct interference with the light, but only a sort of screen, whereas the pricker referred to. actually diminished the light. Dr. Louis had expressed the view that it was a mistake to put the light down, on account of the heat, but the speaker thought it would be agreed that, if the light were obscured in that way, the heat would be reduced as avell. Dr. Louis quite agreed that would be so. His remarks were based on a misunderstanding of the device. It was agreed that further discussion should be adjourned until next meeting. On the motion of the President, a vote of thanks was accorded to Mr. Tate for his paper. Responding, Mr. Tate said he always felt that every member of that institute., especially old members like himself, owed so much to the institutioni that any little ideas they had to. give should be given. Personally, he always felt that he had been indebted to the institute for a great deal of whatever knowledge he possessed, having received it from those members who had gone before them and from those who still remained. There was, apparently, a sort of idea among the younger mem- bers that they must not speak at these meetings. His simple paper was designed to evoke discussion. Every- body must know something that no one else knew, especially on such a subject. "What was wanted was the best, safest, and most convenient light obtainable, and, if by any little improvement that could be made, that ideal could be attained, it behoved them all to try. That question of testing .for gas had been brought very prominently before him during the last two or three years. He had had innumerable instances where depu- ties had gone into places and passed them as free from gas, after which inspectors had entered the places and discovered almost 2| per cent, of gas. There was no Table 1. Effect of Increasing the Initial Temperature on the Low Limit of Complete Propagation of Flame in Methane-Air Mixtures. Test No. Tempera- ture. Pres- sures Analysis of mixtures before sparking. Analysis of mixtures after sparking. Result of observation. Values between which low limit lies. ch4. Air. ch4. co2. Degs. C. Atmos. Percent. Per cent. Per cent. Per cent. Per cent. 1 500 1 . 4*47 95*53 0*58 4*08 Complete propagation 2 500 1 4*27 95*73 0*64 3*85 Do do. 4’00 and 3 500 1 4*00 96*00 0*89 3-14 Do. do. 4 500 1 375 96-25 3*45 0*42 No propagation 3*75 5 500 1 3*50 96*50 3*42 0*18 Do. 6 400 1 4*75 95*25 0*75 3*74 Complete propagation 7 400 — 4*55 95-45 0-65 393 Do. do. 8 400 1 4*47 95*53 4*26 0'41 No propagation 4:55 and 9 400 1 4*25 95*73 4-12 023 Do. [ 4* J7 10 400 1 4*00 96*00 3*88 0*20 Do. 11 400 1 3*75 96*25 3*65 0*20 Do. I 12 300 T 5*15 94*85 0*82 4*36 Complete propagation 13 300 1 4*88 95*02 0*71 4*13 Do. do I 4'88 and 14 300 1 4*75 95*25 4.64 0-13 No propagation I 4*75 15 300 1 4*27 95*73 4*17 0-21 Do. 16 200 1 5*15 94-85 0*20 4-98 Complete propagation 7 5*15 and 17 200 1 4*98 95*02 4*84 0-18 No propagation 5 4*98 18 25 1 5*40 94*60 5*40 0’00 Do. 5*46 and 19 25 1 5*46 94*54 5*47 o*. 0 Do. 20 25 1 5 56 94*44 0*12 5’46 Complete propagation ) 5*56 use in saying that the deputies had not examined the places. One could not examine properly for gas if one had not obscured one’s light. Deputies should be pro- vided with implements that would enable a place to be examined in safety. He thought that nothing in connection with safety lamps' should be patented. He would not think of patenting his little device, even if he knew he could make ^20,000 thereby. He invited the members to try the pricker of the pattern he had described. The meeting then ended. _____________________________ British Columbia’s Coal Production.—In a cablegram, the Minister of Mines, British 'Columbia, estimates that British Columbia produced 7,094,000 tons of coal in 1916, a total which substantially exceeds the 5,638,952 tons in 1915. The coke production amounted to 1,500,000 tons in 1916. and 1,571,181 tons in 1915. Irish Coal Contract Dispute. — In the King’s Bench, Dublin, recently, before Mr. Justice Pirn, in the case of Shannon a. Barkley and Company, an application was made on behalf of the plaintiff, who is a coal factor in Belfast, for an order for discovery of documents against the defendants, who are merchants in the same city. The action was brought to recover damages for alleged breach of contract in the delivery of coal to plaintiff’s order. The plaintiff had been directed by the court .to give particulars as to the alleged breach of contract, and the application for discovery was for the purpose of enabling him to have access to the defendants’ books, with a view to giving the particulars sought. Mr. Justice Pirn made the order sought. EXPLOSIBILITY OF METHANE-AIR MIXTURES? By G. A. Burrell and I. W. Robertson. The experiments detailed were carried out to deter- mine the effect of temperature and pressure on the low limit of complete propagation of flame in mixtures of methane and air. Temperatures up to 500 degs. Cent, and pressures of five atmospheres above atmospheric pressure and 250 mm. below atmospheric pressure were employed. The apparatus used is shown in the drawing. Tbe explosion pipette a had a capacity of 100 c.c. Platinum wires were fused into the upper part. A spi rk from an induction coil, driven by four dry cells, was used to ignite the gas mixtures. An electrically heated oven d surrounded the explosion pipette. The temperatures were measured by means of a platinum-rhodium thermo- couple. Transparent mica plates were used to close tbe upper end of the oven in order to observe the effects of of sparking the mixtures. A reserve pipette b of 200 c.c.’ capacity was fastened to the explosion pipette by means of pressure rubber tubing, with mercury as the confining fluid. The apparatus was made ready for use by raising the levelling bottle c, thereby completely filling the pipettes a and b with mercury, and then lowering it until all of the mercury had fallen from a, leaving a vacuum therein. The stopcock between the two pipettes was then closed and the required gas mixture drawn into b through the free end of the stopcock. After the oven was heated to the required temperature, the gas mixture was admitted into a and sparked after two seconds had elapsed. The flame produced, if any, was observed and the products of combustion analysed. The gas mixtures were ignited by passing through them a spark from an induction coil driven by three small dry cells. Preliminary experiments were performed with a thermo-couple inserted in the explosion vessel a to determine the time required for the gas to attain the temperature of the oven. It was found that this time was less than two seconds after the introduction of the gas. Methane was prepared from the natural gas used at Pittsburg by fractional distillation in a vacuum at low temperatures. The natural gas was liquefied at the temperature of liquid air and as much gas pumped from it with a mercury pump as possible. The distillate was re-liquefied and pumped again. The yield of pure methane was about 85 per cent, of the original volume of the natural gas used. Effect of Increasing Initial Temperature. The results of experiment to determine the effect of increasing the initial temperatures of the mixtures are shown in Table 1. Experiments 1, 2, 3, 4 and 5 show the lower limit of complete propagation with the initial temperature at 500 degs Cent, andthe initial pressure at one atmosphere. As far as the eye could judge, the explosion vessel was completely filled with flame when mixtures containing 4 and 4*27 per cent, of methane was sparked. However, a measurable amount of methane remained unburned, probably due principally to the fact that a small amount of gas was contained in the tube between the stopcock and the electric oven and did not burn. When the methane in the mixture was 3 75 and 3 50 per cent, no flame was observed, although some methane burned, as was shown by the carbon dioxide found upon analysis. According to these results, the low limit of complete propagation is between 3-75 and 4 per cent, when the initial temperature is 500 degs. Cent, and the initial pressure is one atmosphere. At 400 degs. Cent, and at atmospheric pressure a mixture containing 4*55 per cent, of methane completely propagated flame, as far as could be judged by the eye, although 0*75 per cent, methane was not burned. When the methane content was lowered to 4*47 per cent, no propagation was observed. The same was true of mixtures containing 4 27, 4, and 3 75 per cent, methane. , Experiments 18, 19 and 20 were performed to obtain the low limit of complete propagation of methane-air mixtures under ordinary conditions of temperature and of pressure. This value lies, it will be noted, between 5*46 and 5*56 per cent, methane. Undoubtedly, a small * United States Bureau of Mines—Technical Paper 121. quantity of carbon dioxide was formed in experiments 17 and 18, but not enough to detect by the method of analysis used. In each test an analysis was made of the mixture before and after sparking. The sum of the percentages of carbon dioxide and methane should equal the percentage of methane present before sparking. Tbe results of the analyses agreed quite veil. The variation of tbe limits of explosibility with temperature and pressure may be explained on purely thermal grounds-. If ian explosive mixture of methane and air b^ heated the number of collisions between molecules inciecses with rising temperature, and lhe Apparatus for Testing Effect of Temperature and Pressure on Explosibility. speed of reaction increases until a violent reaction and appearance of flame follow. The temperature at which this kind of a reaction takes place is called the ignition temperature. The ignition temperature of methane- air mixtures was found by Dixon and Coward to le between 650 degs. and 750 degs. Cent. Slow comb ration is possible, however, at temperatures below the ignition temperature, depending on the nature of the source of ignition and length of time gas is heated. But in order that flame may be propagated throughout tbe gas mixture the heat of reaction of a layer of gas near the igniter must be sufficient and its rate rapid enough to raise the temperature of the adjacent layer to the ignition temperature. Obviously, the higher the initial temperature the less heat will' be required to raise that of a given mass of the gas to the ignition point, and consequently the smaller is the heat of combustion and the percentage of methane that is required to furnish this quantity of heat. Exposure to High Temperatures without Sparking. A few experiments were performed to show the extent to which combustion would take place in various mixtures of methane and air when subjected to high temperatures without sparking. The results were as follow:— Table 2.—Results of Exposing Methane-Air Mixtures to High Temperatures Sparking. Analysis before ignition. t Pressure. CH4. Air. Atmos. Per ct. Per ct. 1 ... 4*27 ... 95*73 .... 1 ... 4*27 ... 95*73 .... (500 DEGS. CENT.) WITHOUT Analysis after ignition. i------"------Time CH4. CO2. exposed. Per ct. Per ct. Minutes. . 4*21 ... 0*10 ... 0*5 . 3 89 ... 0*40 ___ TO 1 .... 4*60 ____ 95*40 .... 3*74 .... 0*90 .... 30 The results show that no appreciable combustion occurred in the experiments gjiown in Table 1 between the time the gas mixtures were introduced into the pipette and the time they were sparked. In the experi- ments described in Table 1 not longer than 2 seconds was required for the mixtures to attain the temperature of the oven after introduction into the exhausted pipette. Table 1 shows that as much as one-half minute exposure to a temperature of 500 degs. Cent, resulted in only a small amount of carbon dioxide. Effects of Increasing the Initial Pressure. Some experiments were made with the apparatus to determine the effect of initial pressures higher than ordinary pressure on the explosibility of methane air mixtures. The first experiments were made with pressures up to 5 atmospheres, obtained by. raising the levelling bottle of tbe apparatus high enough to give the required pressure. It was found that increasing the initial pressure up to 5 atmospheres had no effect in changing the low limit of complete propagation. In other words, the low-limit value of about 5*5 per cent, methane is true at 5 atmospheres pressure. M. Taffanel has informed the authors that in the case of hydrogen-air mixtures an initial pressure of 40 atmospheres had no effect in changing the limit of inflammability. Effects of Decreasing the Initial Pressure. Experiments were performed to show the sensitiveness to ignition of various methane-air mixtures by deter- mining the least pressures necessary to ignite them