JULY 9TH, 1884. A LECTURE ON THE DOMESTIC USE OF GAS. By HAROLD B. DIXON, M.A. IN venturing to speak to you from a scientific point of view on the domestic use of gas, I hope I may not appear to be approaching a subject of such vital importance to our homes with a light heart, and to be rushing into mysteries where even the initiated speak with fear and trembling; but when I am told for the five hundredth time that the gas is bad, because the gas-flame flickers or roars, and you get blacks on the ceiling; when I find the housemaid for the thousandth time putting the poker against the bars "to. draw the fire," as she calls it; when I find paterfamilias saying he will have his joint roasted with an honest English fire, and will have none of your new-fangled gas-arrangements; I think it is time to speak out. The gas-flame does not roar and blacken the ceiling because the gas is bad, it does so because the gas-burner is unsuitable. The poker does not draw the fire-but I will not enter into that, for I do not want to run my head against a popular fallacy, which does not enter into my subject; but I can assure paterfamilias that he would not know whether his joint were roasted by an honest coal-fire or by a gas-flame, but in the latter case I know he would pronounce the joint to be exceptionally juicy. Now when I say I shall speak of the domestic use of gas VOL. III.-H. L. K from a scientific point of view, I mean that we must start from the commencement, and see what kind of thing coal gas is, and what is the nature of its combustion. Now, coal-gas is a mixture of bodies, but it contains chiefly hydrogen, and bodies called hydro-carbons; they are gases made up of hydrogen and carbon. Coal gas is quite invisible, transparent and colourless; when it burns, the hydrogen burns to water; it forms water by combining with one of the constituents of the atmosphere, and the carbon in the same way-forms carbonic acid, and those are the only two products formed when the coal-gas is properly burnt. So that what you have supplied to your house is a mixture of hydrogen and hydro-carbons; when you light the gas, they burn and produce steam and carbonic acid. But they do more than this, because hydrogen burns more readily than carbon, so that if you have a stream of this coal-gas, of hydrogen and hydro-carbons, coming out into the atmosphere and lighted, the hydrogen burns the faster, and some of the carbon gets left behind unburnt; of course it gets burnt in time, but before it can reach the outer air and be there burnt to carbonic acid, it passes an intermediate stage, when it is in the solid state of little aggregates of carbon, and they are intensely heated and give out light; they finally reach the air outside the flame, and then they burn to carbonic acid. You have to look very steadily at the side of the flame to see the fine film of non-luminous flame surrounding the non-luminous gas-flame, but if you do that, you will see that for about one-eighth of an inch all round the luminous flame you have an outer coating, and there you have the carbon being burnt to carbonic acid. Now there are several ways in which coal-gas may be burnt. Suppose you mix coal-gas with 10 times its quantity of air, and apply a light to it, the whole thing will burn almost directly, and we have what is called an explosion. The air being previously mixed with the gas, each part of it is in close contact with the air requisite to burn it, and you have a flame propagated through it with great velocity, and if it is in a closed vessel you have a report. You have hardly any light, but you have intense heat developed, and the noise which we call an explosion. That is one extreme. Unfortunately we are familiar enough with the fact that coal-gas and air mixed together will explode. Coal-gas by itself of course cannot explode, because it has not the air required to burn it. The flame itself is due to a chemical combination; the particles of coal-gas, that is, the hydrogen and hydro-carbons I have been speaking of, come into collision with particles of the air, those particles we call oxygen, and grappling together with intense energy, they give out light and heat from the force of the shock. I do not propose in more detail to go into the theory of flames, but merely to say that you must have chemical combination, and you must have a combination taking place between gases at a high temperature. Whenever you have that, there you have flame. I told you just now that you may have a sudden flame passing rapidly through a great mass of coal-gas and air mixed together, and have an explosion, or you may have the coalgas supplied through, and pouring out of a pipe, but then it does not mix with air all at once. It meets with the air at the edge of the flame, so that you have coal-gas inside and air outside, and at their union, where they come together, you have this chemical combination, and you have a flame. In this gas-flame you have hydrogen burning to steam, and carbon to carbonic acid. Of course they are quite invisible, but the steam and carbonic acid are pouring away into the air. In the flame there is a considerable area of illuminating surface. That is produced by the solid particles of carbon inside the hydrogen flame heated up to whiteness, not being able to burn, because there is no air there to burn them. It is only when they get to the outside that each little particle burns. But this burner is so arranged that air can be passed to the inside of the flame. At the bottom of the burner there is a hole, so that I can let air in, and as the coal-gas runs up the pipe, it creates a draught at the bottom, and pulls in the air, and you will immediately see the character of the flame is altered. This is a flame in |