Fire and Heat 



117 



glowing splinter. It seems to be like nitrogen, for it extinguishes 

 the fire, and it is certainly not like oxygen, which would have pro- 

 duced a burst of flame. Now introduce a burning splinter or a candle. 

 Do not be alarmed if a slight explosion occurs. Hold the tube securely, 

 always inverted, and observe closely what happens. The flame of 

 the candle is extinguished; but unlike nitrogen, the substance itself 

 burns with a pale bluish flame that runs upward into the tube. Note 

 the heat produced. After the burning ceases, examine the inside of 

 the tube. Is it moist? Does the moisture tend to form drops of 

 water ? 



Oxygen, you have learned, is indispensable to combustion, and it 

 must unite with the burning substance in the tube ; their product is 

 apparently moisture or water. Before you draw a final conclusion, 

 examine the gas collected in the other tube. Remove, close imme- 

 diately with your thumb or a stopper, and invert it to upright posi- 

 tion. Insert a glowing splinter. What is the result? Repeat this 

 until the reaction fails. What substance is this? 



Apparently water can be decomposed into two constituents, 

 one of which is oxygen, as shown by its support of combustion, 

 and the other a gas which does not sustain combustion, but is 

 itself combustible, burning with a pale bluish flame and much 

 heat. If all these points 

 are not clear, repeat the 

 tests with the second tube 

 of substance collected. 



Inflammable air or hydro- 

 gen. It is interesting to 

 find that Henry Cavendish 

 (1731-1810), an English in- 

 vestigator, discovered this 

 combustible gas and care- 

 fully studied its behavior. 

 Having learned the properties which your tests make clear, 

 he called it " inflammable air." He proved that when it burned 

 with the oxygen of the air in a perfectly dry bottle (Fig. 36), the 

 only product of the combustion was moisture, which condensed 

 into small drops of water. The question " by what substances 



FIG. 36. The product of hydrogen 

 burning with air. Enough may be ob- 

 tained in this way to test for its properties. 



