WATER 



135 



tain hydrogen. If it is hydrogen, it will burn with a 

 blue flame that is almost invisible in daylight, and will 

 produce great heat. If the gas escaping from the tube 

 containing the most gas is lighted and a larger long glass 

 tube lowered so as to surround the flame, drops of water 

 will be seen to collect on the inside of the larger tube. 

 This water is a result of the union of the hydrogen with 

 the oxygen of the air. 



The gas in the tube containing the smaller amount 

 will support combustion, if it is oxygen. If a glowing 

 splinter of wood is held at the end of the tube where the 

 gas escapes, it will burst into flame. 



Pure hydrogen can also be obtained by placing pieces of 

 zinc in a bottle, as shown in the illustration, and pouring 



PREPARING HYDROGEN 



on the zinc dilute hydrochloric acid. Collect the gas com- 

 ing from the bottle by allowing it to pass through a tube 

 into another bottle containing water and inverted in 

 the pneumatic trough. Caution. It will be found that 

 if this hydrogen gas is mixed with oxygen and a lighted 

 match placed at the mouth of the bottle an explosion 

 will result, so the gas must be handled with some degree 

 of care. 



