114 Introduction to the Study of Science 



melting. But the part of the candle which has been burned 

 does not become solid. What has become of it? It is com- 

 monly said that it has been burned. The candle as a candle 

 certainly does not exist after burning, but the substances of 

 which it is composed are by no means lost. A burning candle 

 produces light and heat, which may be measured exactly ; but 

 with these we are not now concerned. The products of burning 

 are what we are interested in; and these we must seek in 

 different ways. 



45. Is water a product of combustion ? You have often 

 observed water forming on the bottom of a pan placed over 

 the fire, and perhaps wondered how it came there. Usually 

 the fact is dismissed with the assumption that it must have 

 been on the outside of the pan beforehand. But it is worth 

 investigating to find out whether or not this assumption is 

 correct. A simple way of testing it is this : 



Exercise. Hold a test tube which you have made perfectly dry 

 outside, and which is nearly full of cold water, about two inches above 

 the burning candle, or at such height as will avoid sooting. What 

 appears on the outside of the tube? Can you identify it by touch or 

 taste ? If you should weigh the tube and its contents before and after 

 this experiment, you would find that the weight is increased by the 

 amount of moisture formed on the outside. Where does it come from? 

 Certainly not from the water in the tube. Can it come from the 

 candle? There is no visible sign of water in the candle. May there 

 be some substance in the candle, which in the form of gas combines with 

 oxygen to produce this moisture? 



Moisture, which seems to be one product of the candle burning in 

 the air, may be peculiar to the candle. Try the same experiment 

 with any kind of flame available, as gasoline, kerosene, alcohol flame, 

 or illuminating gas which certainly contains no water. It would 

 hardly be possible to mix these with water and produce a useful 

 flame. You discover by trial that each of them produces moisture 

 which in sufficient quantity may be identified as water. 



Composition of water. It is necessary to find out of what 

 water is composed, so that we may know what in the burning 

 candle unites with oxygen to form water. 



