Eighth Meeting: 6th September, 1886.
Professor F. D. Brown, President, in the chair.
Professor Brown gave a lecture on “The Luminosity of Flames.”
He commenced by pointing out that a flame was the burning of vapour, never the burning of solids, or of a liquid body. He illustrated this by lighting an ordinary candle, and showed how the tallow had to be melted and volatilised before there was a flame. He elucidated the same theory by blowing the candle out and then igniting it immediately with the light two inches away from the wick. He then proceeded to point out that solid bodies sometimes burnt intensely but without flame. This he illustrated with a piece of charcoal burnt in oxygen. Professor Brown then pointed out from these experiments that a flame was a vapour burning in the air, and that there must be a surface where they joined for combustion to take place. By a series of most interesting experiments he showed the hollowness of flame, and that the hollow contained a combustible vapour; and, by another series of experiments, showed that the flame was a shell separating a combustible from a non-combustible substance. He pointed out that
flames were not always luminous, and by a series of experiments he showed that the luminosity of flames arose from solid particles contained within them, which became white-hot. This theory he illustrated by leading the smoke from a turpentine flame into a Bunsen burner, making the flame of the latter luminous: also by scattering powdered chalk in the flame. He gave further illustrations of this theory by the combustion of magnesium and phosphorus, proving that the luminosity was due to the presence of particles. Professor Brown then dealt with the arguments against this theory, as, for instance, the flame from arsenic. This he explained was an oxide, but he could not illustrate it, as without special provision there would be danger from the fumes. He, however, gave an illustration from carbon sulphide, which when applied to the oxygen jar created some sensation. There was a brilliant light for a moment and then a loud explosion, which created some consternation amongst the audience. He, however, showed that even here there was a solid body in the flame. Professor Brown then in a very interesting manner proceeded to show by a series of experiments that the luminosity of the flame of coal gas was due to the carbon particles contained in it.