118 CHEMISTRY. 



is so much heavier than air that it can be poured down- 

 ward from one vessel into another. But if you wish to 

 transfer hydrogen from one vessel to another, you must, as 

 we may say, pour it upward, as repre- 

 sented in Fig. 40. Here the lower ves- 

 sel contains the hydrogen. This be- 

 ing only one fourteenth of the weight 

 of air, goes quickly upward into the 

 upper vessel, forcing the air that is in 

 it downward. You can not see the 

 gas pass, because it is invisible ; but 

 a similar phenomenon can be made visible by emptying a 

 vessel of oil into another under water. Here the lighter oil 

 passes upward into the upper vessel, forcing the water down 

 out of it, just as the hydrogen does to the air. 



147. Ballooning. Hydrogen gas has been much used in 

 balloons. Montgolfier, a Frenchman, who was the first to 

 make an ascent with a balloon, inflated it with heated air. 

 This was in 1783, thirteen years after the discovery of hy- 

 drogen by Cavendish. Hydrogen is much better than heat- 

 ed air for inflation on two accounts first, because it is so 

 much lighter ; and, secondly, because it retains its lightness, 

 while the heated air becomes heavy by being cooled as the 

 balloon is on its passage. Hydrogen was used in ballooning 

 the same year that Montgolfier made his ascent, and yet 

 Montgolfier balloons continued to be used to some extent 

 even as late as 1812. Even so late as 1847, strange as it 

 may seem, an ascent was made with one of these balloons 

 by a Frenchman, Godard, who fell into the Seine, but was 

 saved from drowning. At the present time gas balloons 

 alone are used, and illuminating gas, a mixture of hydro- 

 carbons, is employed for inflation, as this, though heavier 

 than pure hydrogen, is sufficiently light, and can always be 

 readily obtained from neighboring gas-pipes. Ascending 



