The Story of a Tinder-box

by Charles Meymott Tidy

Fig. 36.

Just let me say a few words about the grand result—the consummated work of the tinder-box. A flame is a very remarkable thing. It looks solid, but it is not solid. You will find that the inside of a flame consists of unburnt gas—gas, that is to say, not in a state of combustion at all. The only spot where true combustion takes place is the outer covering of the flame. I will try to show you some experiments illustrating this. I will take a large flame for this purpose. Here is a piece of glass tube which I have covered with ordinary white paper. Holding the covered glass tube in our large flame for a minute or two, you observe I get two rings of charred paper, corresponding to the outer envelope of the flame, whilst that portion of the paper between the black rings has not even been scorched, showing you that it is only the outer part of the flame that is burning (Fig. 35). The heat of the flame is at that part where, as I said before, the combustible gases come into contact—into collision with the atmosphere. So completely is this true, that if I take a tube, such as I have here, I can easily convey the unburnt gas in the centre of the flame away from the flame, and set fire to it, as you see, at the end of the glass tube a long distance from the flame (Fig. 36). I will place in the centre of my flame some phosphorus which is at the present moment in a state of active burning, and observe how instantly the combustion of the phosphorus ceases so soon as it gets into the centre of the flame. The crucible which contains it is cooled down immediately, and presents an entirely different appearance within the flame to what it did outside the flame. It is a curious way, perhaps you think, to stop a substance burning by putting it into a flame. Indeed I can put a heap of gunpowder inside a flame so that the outer envelope of burning gas does not ignite it (Fig. 37). There you see a heap of gunpowder in the centre of our large flame. The flame is so completely hollow that even it cannot explode the powder.

Fig. 37.

Fig. 38.

I want you, if you will, to go a step further The heat of the flame is due, as I explained in my last lecture, to the clashing of molecules. But what is the light of my candle and gas due to? The light is due to the solid matter in the flame, brought to a state of white heat or incandescence by the heat of the flame. The heat is due to the clashing of the particles, the light is due to the heated solid matter in the flame. Let me see if I can show you that. I am setting free in this bottle some hydrogen, which I am about to ignite at the end of this piece of glass tube (Fig. 38 A). I shall be a little cautious, because there is danger if my hydrogen gets mixed with air. There is my hydrogen burning; but see, it gives little or no light. But this candle flame gives light. Why? The light of the candle is due to the intensely heated solid matter in the flame; the absence of light in the hydrogen flame depends on the absence of solid matter. Let me hold clean white plates over both these flames. See the quantity of black solid matter that I am able to collect from this candle flame (Fig. 38 B). But my hydrogen yields me no soot or solid matter whatsoever (Fig. 38 A). The plate remains perfectly clean, and only a little moisture collects upon it. The light that candle gives depends upon the solid matter in the flame becoming intensely heated. If what I say be true, it follows that if I take a flame which gives no light, like this hydrogen flame (Fig. 39 A), and give it solid particles, I ought to change the non-luminous flame into a luminous one. Let us see whether this be so or not. I have here a glass tube containing a little cotton wadding (Fig. 39 B a), and I am about to pour on the wadding a little ether, and to make the hydrogen gas pass through the cotton wadding soaked with ether before I fire it. And now if what I have said is correct, the hydrogen flame to which I have imparted a large quantity of solid matter ought to produce a good light, and so it does! See, I have converted the flame which gave no light (Fig. 39 A) into a flame which gives an excellent light merely by incorporating solid matter with the flame (Fig. 39 B). What is more, the amount of light that a flame gives depends upon the amount or rather the number of solid particles that it contains. The more solid particles there are in the flame, the greater is the light. Let me give you an illustration of this. Here is an interesting little piece of apparatus given to my predecessor in the chair of chemistry at the London Hospital by the Augustus Harris of that day. It is one of the torches formerly used by the pantomime fairies as they descended from the realms of the carpenters. I have an alcohol flame at the top of the torch which gives me very little light. Here, you see, is an arrangement by which I can shake a quantity of solid matter (lycopodium) into the non-luminous alcohol flame. You will observe what a magnificently luminous flame I produce (Fig. 40).

Fig. 39.