52-55] PROPERTIES OF HYDROGEN 21 



testing until it is quite free from air, then collect a few 

 cylinders as described in paragraph 31. 



52. Hydrogen burns but does not support combustion. 

 As soon as a cylinder is full of hydrogen remove it from 

 the trough, keeping its open end downwards, and thrust a 

 lighted taper into it. The taper will be extinguished, but 

 the hydrogen itself will burn with a flame which is scarcely 

 visible. 



53. Hydrogen is the lightest substance known. Fill 

 another cylinder with hydrogen and pour the gas upwards 

 into a cylinder which contains nothing but air. Then test 

 each cylinder with a lighted taper. The one which formerly 

 contained the gas will have no effect on the taper, whilst 

 the one which formerly contained no hydrogen will give a 

 sharp explosion, showing that hydrogen is lighter than 

 air. 



54. Fill a short thick cylinder with water, then invert it 

 in a dish of water. Displace about two-thirds of the water 

 with hydrogen and the rest with oxygen. Allow the gases 

 to stand for a few minutes to mix thoroughly, then apply a 

 lighted taper ; a loud explosion will take place, due to the 

 gases combining to form water. 



55. The energy of the combination of the gases in the 

 last experiment prevents the water formed from being readily 

 collected. But if hydrogen is allowed to combine with the 

 oxygen of the air under suitable conditions the water may 

 be collected. Replace the bent delivery-tube (fig. 21) by 

 a straight piece of glass tube 6 inches long. Allow an 

 energetic stream of hydrogen to pass for some minutes, 

 then ascertain that the hydrogen is free from air by the 

 following test. Hold a small test-tube over the end of the 

 upright tube for half a minute, close the mouth of the tube 

 with the thumb and apply a light. If the gas is free from 

 air it will burn quietly up the tube j if it explodes with a 

 squeaking noise continue the evolution of the gas until the 



