GASES 157 



advantage of lamp chimneys, smoke-stacks, tall chimneys, and 

 other devices for causing better combustion. 



Cooling the candle flame by thrusting into it a cold sub- 

 stance, such as a bar of metal, causes it to smoke. Carbon burns 

 only at a high temperature, and in this case much heat is lost to 

 the cold substance. 



Those substances which contain much carbon, such as tur- 

 pentine, camphor, and sealing wax, may be made to give out a 

 very black smoke. The carbon may be caught as soot or lamp 

 black, which subsequently can be burned. 



In general, we depend upon the carbon for the light in the 

 illuminating flame, but in the calcium light a very hot flame ia 

 used to heat a piece of lime (calcium oxide) to a white heat, 

 which gives out the bright light. In the stereopticon, oxygen and 

 illuminating gas are used to heat the lime. In the class room a 

 blow-pipe and an alcohol flame can be made to give a bright 

 glow to a piece of lime sufficient to illustrate this point. In 

 burning a bit of magnesium ribbon, it is the white dust, the 

 magnesium oxide resulting from the combustion, that gives the 

 light. 



The foregoing should be broken up into many lessons. These 

 will suggest many others. The applications of what has been 

 given are very numerous, and if well followed out will make clear 

 many things in every day's experience with lights and fires. 



