58 Mr H. H. Blackadder oji the Combustion of 



alcohol be brought to the window, the flame becomes wholly in* 

 visible, not a vestige even of the white portion is to be discerned ; 

 so that any one ignorant of its presence, would almost inevita- 

 bly meet with an accident, or might be induced to lay hold of 

 the burner. This simple experiment will render the existence 

 of an invisible, though intensely hot flame, sufficiently intelli- 

 gible. The surface of the flame of a candle, where the com- 

 bustion is most intense, is the hottest. Where the combustion 

 is most intense, the flame has a pale blue colour, and when this 

 colour comes to be contrasted with intense whiteness, it is too 

 weak to make a sensible impression on the retina. By means of 

 opaque skreens, the attenuated brush may be seen extending all 

 over the flame ; but its presence may also be detected, by chang- 

 ing its colour in a way afterwards to be described. 



The colour of the light that is extricated in a flame, depends, 

 1st, On the mode of combustion ; or, 2d, On the presence of 

 some foreign body or extraneous ingredient. 1. When alcohol 

 or rectified spirit, having a specific gravity of about 835, is 

 burned in a lamp without a wick, and with a half inch flame, 

 or when it is burned on a flat surface of glass, the flame is alto- 

 gether of a blue colour. Again, when in burning the same 

 fluid with the glass-burner, the flame is enlarged to an inch, or 

 an inch and a half in length, a considerable quantity of white 

 light is extricated. Lastly, When the extremity of the glass- 

 burner is brought to a red-heat, or thereby, by holding it in the 

 edge of a blue spirit flame, portions of the alcohol are succes- 

 sively exploded as they come into contact with the heated ex- 

 tremity of the burner, and then much yellow hght is extricated. 

 We have thus blue, white, and yellow light extricated during 

 the combustion of the same fluid, and depending wholly on the 

 mode of combustion. 



Oil may also be burned so as to give out either a blue, a blue 

 and white, or a blue and yellow flame. When oil is burned in 

 a lamp without a wick, so as to give a large flame, the light ex- 

 tricated is blue, with a great prpportion of white. But, if the 

 stop-cock be cautiously turned, the white light diminishes, and 

 at length there is only a blue flame. By again increasing the 

 flow of oil, a spot of yellow light appears in the centre of the 

 blue; and by stiU farther increasing the supply, the white, 



