208 Domestic Science 



more steadily and, if left undisturbed, will continue 

 burning till the candle is entirely consumed. In the 

 first case the candle had to burn in what was 

 practically a limited supply of air, for very little fresh 

 air is able to force its way down the lamp-chimney 

 against the stream of hot air and products of com- 

 bustion proceeding from the flame. 



In the second case, fresh supplies of air passed in 

 through the air-space beneath the chimney, and thus a 

 continuous current passed up the chimney. To show 

 the existence of this air-current let us try 



EXPERIMENT 76. Arrange the candle and chimney 

 as in Fig. 62. Light a wax-taper, and when well alight, 

 blow it out. Place the smoking end near the air-space 

 between the chimney and block. Note the direction 

 taken by the smoke. 



(This should be done in a room free from draughts, 

 or the observation made may not be very definite.) 



140. From the above experiments it is clear that 

 air is necessary for the burning of a candle to take place. 

 Other combustible bodies such as coal, wood, coal-gas, 

 brimstone, and paraffin oil, also require a good supply 

 of fresh air in order that their burning may be continuous 

 and complete. 



While dealing with this matter, we may note that 

 the two simple experiments just performed illustrate 

 the value of a fire in an open fireplace as a ventilating 

 agent. The fire corresponds to our candle, the house- 

 chimney to our lamp-chimney, and the openings in the 

 walls of the room (e.g. the opened part of the window, 

 if any, and the cracks beneath and around the doors 

 and the window-sashes) to the air-space provided 

 between lamp-chimney and block. Fresh air is con- 

 tinually entering through these openings while the fire 



