THE CHEMISTRY OF WATER. HYDROGEN. 



119 



in balloons is exceedingly dangerous. We have seen a list of 

 the most famous aeronauts, and of the whole forty-one there 

 were fourteen killed, and various injuries were received by 

 many of the others. Plainly, then, an ascent ought never 

 to be made for mere show, and the only useful purpose that 

 ballooning has yet subserved is for observation in time of 

 war. During the war of 1871 between France and Prussia, 

 both armies made use of balloons to a considerable extent. 

 The people shut up in Paris sent out balloons nearly every 

 day. 



148. Combustibility of Hydrogen. While oxygen is the 

 grand supporter of combustion, hydrogen 



itself burns. The flame is very pale, and . 

 attended with so little light as to be al- 

 most invisible on a bright day. In Fig. 

 41 you have represented hydrogen burn- 

 ing from what has been called the "phi- 

 losopher's candle." The materials for 

 the production of hydrogen gas, noticed in 

 143, are placed in the bottle, which has 

 a tube fastened into the cork. Here, too, 

 carelessness may occasion an explosion. 

 The air must be expelled from the bottle 

 before the "candle" is lighted. 



149. Hydrogen Bubbles. The lightness 



and combustibility of hydrogen may both be very prettily 



exhibited by having a tobacco-pipe, b, Fig. 



42, attached to the stop-cock, a, of an India- 



rubber gas-bag filled with hydrogen. If 



the pipe be introduced into soap-suds while 



the stop -cock is opened and the bag is 



pressed upon, soap-bubbles will rise in the 



air, which, on being touched with a light, quickly burn with 



a slight explosion, occasioning a popping sound. 



Fig. 41. 





