September 16, 1916. THE COLLIERY GUARDIAN. 503 be granted tc manufacturers that the domestic fire was a very bad offender. If one-fifth of the output of coal was used for domestic fuel, that fuel was certainly creating a good deal more than one-fifth of the smoke, but it w*as a more difficult problem to stop domestic smoke than industrial smoke. Every chemist must feel strongly that the present way of using coal, even if the best price were got for it, precluded a long future, and this fact must be faced and the difficulties sur- mounted. Although it was true that, at present, atmo- spheric nitrogen was not being extracted on a large scale and used for making nitric acid, experiments were being made in England, and he hoped that very shortly a workable plant would be seen, in more than one town, for making nitric acid directly from the atmo- sphere. lie had already seen' this being done on a reasonable scale. Dr. Des Vceux, as chairman and treasurer of the London Smoke Abatement Society, said it gave him a certain amount of malignant pleasure to address the meeting, because for 20 years chemists and engineers had refused to accept an invitation to join the committee of that society. Having regard to the work which the society bad done, he was a little disappointed that no reference had been made to it, either in the committee’s report or in the various speeches. Nevertheless, he claimed that the work of the society had resulted in a vast improvement in the atmospheric conditions in London. As an instance, he mentioned the Central London Railway power station at Shepherd’s Bush, where the adoption of means to prevent smoke emission had saved 600 tons of coal per week. He believed it had been accomplished, half by mechanical stoking and half by educated hand stoking. The domestic question had also been tackled, but -it was a much more difficult one, and the statistics went to show that something like 1,000 tons of coal were thrown into the London atmo- sphere from domestic chimneys every year. Dr. E. F. Armstrong spoke of the economies which could be effected in steam raising plant by strict atten- tion to matters of detail. In this way, works for w’hich he was responsible had saved many thousands of tons a year, and it was a real economy to have a highly paid scientific man to look after this matter. He hoped Prof. Bone would be encouraged in his pioneer work of train- ing this class of man to be sent out all over the country. Smokeless Firing. Mr. C. E. Stromeyer said that the Manchester Steam Users’ Association a good many years ago carried out 400 experiments on coal consumption, and, as a result, sent men round the country to show how* stoking should be done. They were great advocates of the side firing, which was a smokeless way of firing, but the thing fizzled out, because steam users did not care how they got steam so long as they got it. Probably the present inclination for economy was due to the very high price of coal. One effect produced in the anti-smoke move- ment, especially in London, was that householders were practically forced to burn the very highest class of coal. In Manchester it was impossible to burn dirty coal owing to the grates. Similarly, present-day boilers having to be worked ata higher rate than they were really intended for, it was necessary to burn a higher quality of coal, and that was one reason why comparatively valueless coal was left on the colliery owners’ hands. There was no reason why these coals should not be burned without smoke. Col. Blackett, as representing the coal producer and a colliery manager, said it appeared to him that collieries had been asked for too many years to produce too much coal at too cheap a rate. He would not suggest that they had been casting pearls before swine, but they had at any rate been casting valuable coals before fools very largely. He did not agree that grates should be built to burn the veriest rubbish, because the collieries them- selves were burning this rubbish (on account of its being unmarketable) simply by putting in suitable fur- naces. Those collieries who had put down coke ovens did not do so to get coke or by-products, but were driven to do it to get rid of the small coal. They were, as a matter of fact, able to sell their coke more easily than they could small coal, and in the past this small coal had been laid in heaps on the railways, and some of it could be dug up at the present time. After having improved the coke ovens to get as much coke as possible, when the demand fell off, as it probably would do, the chemist apparently would calmly say that they should have recovered the by-products. His answer to that was that he would prefer to go back to the early position, and would sell his small coal to anyone who would buy it, and let them do the best they could with it; but the colliery owners should not be reproached now because they had not got the fine results which some people thought they ought to have done. It was not the business of colliery owners to go in for chemical manufacture at the colliery. That was done by the large colliery owners who were iron masters, and who had their own steel works to administer, and that was all right; but they had never yet got to know their economic position when they were producing all those different things. The only way to do it was, he said, by separate works, taking the coals that the colliery could give and dealing with them in the way which had been suggested. Prof. Henderson said chemists regarded coal as the storehouse of energy, and they did not want the valuable by-products thrown away, as that meant throwing away at the same time a large chemical industry. As to the domestic problem, he looked forward to low tempera- ture distillation to produce a smokeless fuel which would very largely solve that problem. (To be continued.) INFLUENCE OF PRESSURE ON THE ELECTRICAL IGNITION OF METHANE* By W. M. Thornton, D.Sc., D.Eng. Methane. Methane, CH4, is the lightest and simplest of the paraffin series of hydrocarbons, having a density 0’55 that of air. At atmospheric pressure it ignites between 650 and 750 degs. Cent. Its limits of inflammability are 5’6 and 13*8 per cent, of the gas in air when ignited at the open end of a horizontal tube. If the temperature is raised before ignition, mixtures as weak as 3 per cent, are inflammable. It has at high pressures a remarkable affinity for oxygen, much higher than has hydrogen, and there is some evidence of this at atmospheric pressure. It is nevertheless more difficult to ignite by electric sparks. Pit gas in England derives its inflammability from methane. Ordinary house gas contains from 30 to 40 per cent, of methane, together with hydrogen, carbon monoxide, and smaller quantities of unsaturated hydrocarbons. The present experiments on the influence o 80 20 40 60 Lb. per square inch. Fig. 1.—Change with Pressure of Least Alternating Current Igniting at Break a 25 per cent. Mixture of Hydrogen in Air. of pressure on gaseous ignition were made with methane, in the mixture 9’5 per cent, in air, which just gives perfect combustion. The Electrical Sparks Used. The limits of inflammability of gases have been measured mostly at atmospheric pressure and by streaming spark discharge. At lower pressures igni- tion is more difficult, and fails at some definite pressure, which depends on the kind of igniting spark. A stream of sparks, or one drawn out slowly, has all the thermal properties of a steady flame, but in modem practice ignition is usually by single electrical impulses. Four kinds of single spark may be used for experi- mental ignition, each of which has characteristic features, and all but one of which is in practical use. These are :—(1) A transient electro-magnetic impulse; (2) the discharge of a condenser placed across the gap; (3) the short arc formed at the point of breaking a con- tinuous current circuit; (4) the same with alternating current. The last two differ so much in some of their 11 10 12 9 8 7 6 4 5 2 1 o- 0-4 1-2 11 o L o Amps. 13 --- 0-6 0-8 1-0 Atmospheres. Fig. 2.—Ignition of Methane in Air by Impulsive Sparks, Platinum Points. effects that they have been examined separately. In each of these groups there are sparks which do not ignite the most inflammable mixtures of highly combustible gases and air. Although an impulsive or jump spark starts by ionisa- tion, usually across a fixed gap, its igniting power has been shown to follow a different law from that of rupture alone. Condenser discharge passes just before metallic contact of two terminals which are being brought together, and when the charging voltage and the poles are the same throughout, occurs at the same spark length. It is, however, an exceedingly rapid effect, and it is probable that the ionisation with which it starts is masked by the intense activity of the discharge, so that the ultimate ignition is proportional to its energy or power. * Paper read before Section G of the British Association at Newcastle. The two circuit break sparks are less simple. They are streams of electrons following a path which becomes more difficult as the gap opens. The momentum of the electrons of this stream is comparable with that of 'the molecules of gas around it. The latter, therefore, pene- trate the arc, and are exposed to the dissociating influence of its high temperature. The conditions of ignition arise from the collision of the gas with the ions in the arc. The action is no doubt partly thermal and partly ionic; in some cases ignition is proportional to the current; in others its change is proportional to the current squared. The extraordinary variety of the reaction between gas and spark, indicated by the limit- ing electrical conditions of ignition, Is not to be accounted for on a simple thermal basis. Ignitibn by Impulsive Coil Discharge. Ignition at atmospheric pressure has been showm to have steps, which appear, as the percentage of gas is varied, in certain well-defined mixtures. The precise 30 25 35 20 1-5 10 0:5 Amps. 4-0 r 0 ------i--------------------------------------------------- 0 10 20 30 40 50 60 70 80 90 100 Lb. per square inch. Fig. 3.—Impulsive Sparks, Nickel Points. Microfarads. JO 20 30 40 50 60 70 80 90 100 Lb. per square inch. Fig. 4.—Condenser Discharge, 150 volts, Platinum Points. origin of these steps is still obscure, but there can be no doubt that they are examples of selective action which occurs at certain frequencies of collision between the molecules of combustible gas and oxygen. The evidence for this is tw'ofold. In the first place, the steps, either up or down, occur in mixtures in which the proportions of the atomic volumes of the two gases can be represented by whole numbers. In methane, hydrogen, and cyanogen, for example, there are distinct steps, as in Table I., the limits being regarded as steps. Table I. Methane, CH + . Hydrogen, H2. Cyanogen, C2N2. O:CH4 •£air.StePH 2 : q Per c. * in air. Step. O :C !2N2 Per c. in air. Step. 9 ... 5’55... 5'6... i ... 9*3.. .c. 9... 5 . 7*6.. . 7*5 4 ... 9*35... 9*8... 1 ...29*2 .. 29 4 ’ . 9*3.. . 9*0 7/2 ... 10*5 ... 11*0 .. 2 ...45*2 . 45... 3 . . 12*2.. 12 0 3 ... 12 0 ... 12’0... 3 ...55*2 .. 54... o . 17T.. . 17*5 5 2 ... 15*0 ... 14*8... 4 ...62*2 .. — 1 .’ 29*2 . 29*0 — — — 5 ...67*4 .. — . 35*4.. . 34*5 — — ... — 6 ...71*2 .. c. 70... 5 . 38*0.. . 38*0 These w’ere, however, not all obtained with the same kind of ignition. The occurrence of the steps in some