Fire and Heat 71 



could not be increased by longer heating. A lighted splinter 

 was thrust into the dish and the fire was extinguished at once. 

 This proved that the remaining air does not support combus- 

 tion. The experiment also proved that only a portion of the 

 air is involved in the process of burning. It must be, so La- 

 voisier concluded, this portion of the air which is added to the 

 weight of the products of combustion. 



34. Air and combustion. It has been proved by the in- 

 vestigations of later scientists that only a small proportion oi 

 the air combines with burning substances, and that it is this 

 proportion which makes the products of combustion weigh 

 more than the original combustible materials. In our study 

 we shall seek to demonstrate this fact clearly and also to de- 

 termine how much of the air is used in combustion and how 

 much is not, or how much supports combustion and how much 

 does not. We shall also try to learn by observations and ex- 

 periments what are the essential properties of these two parts 

 of the air, taken separately or mixed. 



It will be worth while to demonstrate the fact that air does 

 combine with substances in being burned, and that the products 

 of combustion weigh more than the substances burned. The 

 following experiment will present a striking illustration of the 

 important facts. 



Exercise : Weighing products of combustion. Fit a wire gauze 

 cone snugly inside a lamp chimney about one third of the distance 

 from the bottom (Fig. 19). Fill the chimney above the gauze with 

 pieces of caustic soda (sodium hydroxid), which will absorb the prod- 

 ucts of burning. Fasten a short piece of a candle on a cork large 

 enough to fit the lower end of the chimney, and into the sides of which 

 notches have been cut to allow the air to pass through. Put the cork 

 with candle into the chimney and stand the whole thing on one arm 

 of a balance. Balance it exactly with weights and very small shot or 

 dry sand. Then light the candle and let it burn in the chimney on 

 the scale arm. What happens? Does the result indicate that the 

 products of combustion weigh more than the visible materials before 

 being burned ? 



