WATER AND THE ELEMENTS COMPOSING IT 237 





or two bottles. When the bottles have been filled, it is better 

 not to remove them from the water until you want to use 

 them. Collect also a soda-water bottle half full of the gas. 



EXPT. 240. Test one jar of the gas by means of a lighted 

 match or taper as in Expt. 238. Observe that the gas 

 burns around the mouth of the jar but that the taper is 

 extinguished, but on being taken out, again becomes alight on 

 passing through the flame of the burning hydrogen (Fig. 121). 



Flo. 121. Hydrogen burns, but 

 extinguishes a Flame. 



A/xL 



FIG. 122. Illustration of Low 

 Density of Hydrogen. 



EXPT. 241. Take a full jar of the gas and hold it mouth 

 upwards below a second smaller jar held mouth downwards as 

 shown in Fig. 122. On testing with a lighted taper observe 

 that the gas has left the lower jar and filled the upper. Many 

 experiments, as the filling of balloons or soap bubbles, may 

 also be performed to demonstrate the extremely low density 

 of hydrogen. 



EXPT. 242. Wrap your hand well in a duster and with it 

 hold the soda-water bottle. Take it out of the water so that 

 the water runs out, and the bottle is now filled with a mixture 

 of hydrogen and air. Apply a light and you will not fail to 

 observe that an explosion results. 



EXPT. 243. Apply a light to the end of the delivery tube 

 and allow the hydrogen to burn. Observe that it burns with 

 a pale blue flame, which after a time becomes yellow. As 

 this colouration does not occur however until the glass becomes 

 hot, we must regard it as due to the glass. 



