Mr Blackadd^r 07i the Constitution ofFiame. 231 



wiil inflame. The flame of the oil that is burned in the lamp 

 will be extinguished ; but the flame of the alcohol will evaporate 

 the oil as it issues from the burner, and this vapour, on coming 

 into contact with the inner surface of the blue flame, will under- 

 go combustion, giving out much white light. In such a case^ 

 the cone of white light from the combustion of the vapour of 

 oil, keeps distinct from the white light of the flame of the alco- 

 holic vapour. 



This experiment has been repeated in a variety of ways, 

 and the result has always been the same ; and hence we are ne- 

 cessarily led to the conclusion, that the vapour in the interior of 

 a flame is incapable of supporting combustion. It is certain, 

 however, that some oxygen is always present in that vapour, 

 for oils and alcoholic fluids always contain some air in a state of 

 mechanical admixture ; and oxygen is understood to be a consti- 

 tuent part of all of them. 



The apex of a spirit flame is the hottest, or is the part at 

 which a solid body is raised to the highest temperature ; and 

 partly for this reason, that less heat is carried off* by the air 

 with which the solid body is surrounded, than at the other parts 

 of the flame — the vapour discharged from the flame being 

 itself at a very high temperature *. The upper part of the flame 

 oi a candle communicates less heat to a solid body than its middle 

 part, where the blue portion terminates. This seems to pro- 

 ceed, in some measure, from the deficiency of hydrogen in the 

 upper and most luminous part of the flame ; and hence, at that 

 part a blowpipe, the use of which infers a greater supply of air, 

 has comparatively but a trifling effect. 



When the opaque white vapour formerly described is burned, 

 so as to produce a white conical flame, the vapour is observed to 

 project into the interior of the flame like a white wick, tapering to 

 a small point ; hence, of a supposed transverse section of a flame, 

 the coldest point would be in the centre. Much heat is con- 

 sumed at the inferior part of a flame ; the burner or wick-hold- 

 er carries off no inconsiderable quantity, and much is consumed 

 in converting the combustible body into vapour. It is an old 

 observation, that a common lamp will burn in air that will ex- 



• In the centre of a conical spirit flame, the heat diminishes from the apex to 

 the mouth of the hurner, near which glass acquires what is termed a dark cherry- 

 red. 



