X 64 Mr H. H. Blackadder on the Combustion of 



brought to the marghi of the blue flame, produces a discharge 

 of hght of a fine yellow colour ; and, in this case, no moisture 

 can be present. In this way a beautiful flame, of a yellow co- 

 lour from the base to the apex, may be produced, and which is 

 altogether free of any unsteady or flickering motion. 



When a piece of wood that has been carbonized in a spirit 

 flame, and completely extinguished, is brought under a blue 

 flame, a very slight motion given to the wood will be followed 

 .by an extrication of yellow light ; and by rubbing two such 

 pieces of wood, the one upon the other, under the flame, the 

 whole of the latter will acquire a yellow colour. Scraping the 

 carbonised wood with a knife produces a similar eff*ect ; but, in 

 this case, larger particles are also separated, which give out 

 light of a brilliant yellow colour, and much better suited for 

 the purpose of illumination, than the dull mat yellow of di- 

 luted alcohol, or that produced by the smoke, &c. of carbonized 

 wood above described. For, in both these cases, the light is si- 

 milar, and proceeds from a modification of the same part of the 

 flame. By means of carbonized wood, &c. the exterior attenu- 

 ated brush-flame of a candle or lamp may be rendered visible all 

 over the flame, a yellow colour being communicated to it. It 

 may be remarked, that there is reason to believe that pure carbon 

 •would not produce the effects above described ; but that has 

 not been procured for experiment. If, when a blowpipe is 

 used with a candle, the wick be cut short, so that the stream of 

 air may pass through the white part of the flame, the jet has 

 a fine blue colour : when the jet has a red or reddish-yellow 

 colour, it will be found that particles of the carbonized portion 

 of the wick, or of soot, are carried off by the current of air 

 from the blowpipe ; and whether a blowpipe or bellows be 

 used, the yellow light is similarly produced in all cases in which 

 the combustion is supported by solid carbonaceous substances. 

 ' When a wire or rod of glass is introduced into a blue flame, 

 yellow light is commonly extricated, and this always proceeds from 

 some foreign substance on the surface of these bodies, such as con- 

 densed smoke, dust, &c. ; it is almost impossible to handle glass or 

 unpolished metals, particularly when the hands are hot, without 

 leaving condensed perspiration on their surfaces. An oppoi*- 

 tunity occurred last summer, of pointing out this circum- 

 stance to Dr Brewster, to whom had been exhibited, and with 



