COMBUSTION. 61 



ing flame; the combination of carbon with oxygen 

 proceeds slowly and steadily, the carbon continuing 

 to glow until all is consumed ; hydrogen, on the other 

 hand, being a gas, mixes and combines with oxygen 

 more rapidly, burning at once, with a flame. 



93. All organic substances burn with a flame, and 

 this alone is a proof that they contain hydrogen, 

 because under ordinary circumstances the other ele- 

 ments of vegetable matter could not cause flame; and 

 whenever the flame is bright, we are sure that it con- 

 tains a good deal of carbon, for the flame of pure 

 hydrogen is very pale indeed, and the brightness of 

 a flame, such as that of a candle, is entirely due to 

 the carbon contained in the tallow, which is burned 

 at the same time with the hydrogen, both combining 

 with oxygen. 



94. As the products of the combustion of a candle 

 are carbonic acid gas and water, it would be natural 

 to expect that a cold substance held over the flame of 

 a candle would take from the vapor of water thus 

 formed, the heat necessary to its existence in the 

 state of vapor, and consequently condense it into 

 the fluid form. This is an experiment which may 

 very easily be made, for we have only to hold a cold 

 glass at a little distance above the flame of the candle, 

 and we shall soon find it lined with a fine dew of 

 water condensed in this manner. 



95. There are several important facts to be ob- 

 served connected with the combustion of a lamp or 

 candle. The wax, tallow, or other combustible sub- 



6 



