588 FOURTH REPORT — 1834. 



The chlorine and antimony found by experiment are, as was 

 to be expected, a little less than is indicated by theory, causing 

 the amount of oxygen to appear greater than it ought to be.* 



On the phcenomena and products of a low form of Combustion. 

 By Charles J. B. Williams, M.D. 



It must have been often observed, that after a candle is ex- 

 tinguished in a dark room, if no spark be left on the surface, 

 the wick continues to be, for a few instants, faintly luminous. 

 This phaenomenon attracted the author's attention many years 

 ago, and on investigating the matter further, he found that 

 wax, tallow, oil, resin, sealing-wax, and many other compound 

 inflammables, are luminous in the dark, when heated to a point 

 considerably below redness. A bar or mass of iron, heated to 

 incandescence, and then allowed to cool till it ceases to give 

 out light in a dark place, affords the most convenient means of 

 exposing substances to the degree of heat required for this 

 phaenomenon. If small portions of wax or tallow be thrown on 

 this iron, they give out a pale bluish light, which, if the heat 

 approaches to incandescence, assumes the form of a lambent 

 flame. Various animal and vegetable oils, resins, lac, caout- 

 chouc, cotton, hemp, linen, paper, flour, starch, gum, silk, 

 cloth, leather, hair, feathers, and almost all compound com- 

 bustibles, exhibit, in various degrees, the same phaenomenon. 

 Sugar does so very slightly. Camphor and other volatile matters, 

 and olefiant gas, may be made to show the light by bringing 

 the vapour or gas into contact with a hot iron held over them. 

 A short statement of the most material of these facts was pub- 

 lished in the Annals of Philosophy for July 1823. The author 

 has lately found that some of them were noticed by Mr. T. 

 Wedgwood, in the Phil. Transactions for 1798, and were by 

 him suspected to be " some kind of inflammation." The lumi- 

 nous appearance has generally, however, been considered to be 

 of the nature of simple phosphorescence, like that of fluor 

 spar and other minerals when heated. These substances 

 give out light independently of access of air, and under water 

 or oil ; and the cause of this singular property, to which the 

 term phosphorescence has been applied, is wholly unknown. 

 On comparing this phaenomenon, however, with that of heated 

 inflammables, the author saw enough difference to induce the 

 belief that they are not similar, but that the latter is owing to 

 a kind of low combustion. 



• For a fuller account of these experiments sec Edinburgh Journal of 

 Science, January 1835. 



