98 



A YEAR IN SCIENCE 



the flask with a rubber stopper, fitted with a thistle 

 tube through which acid may be poured into the flask, 

 and a short glass delivery tube through which the 



Fig". 40. 



Preparation of hydrogen from hydrochloric acid and 

 zinc. 



gas may escape. When the zinc comes in contact with 

 the acid, a chemical action takes place by Which 

 hydrogen is set free. Any acid will do, though hydro- 

 chloric acid is the one most generally used. Hydro- 

 chloric acid is a compound of the elements chlorine 

 and hydrogen. When the acid and the metal come in 

 contact, the metal displaces the hydrogen and com- 

 bines with the chlorine to form zinc chloride. 

 Zinc + hydrochloric acid = zinc chloride + hydrogen. 



Zn + 2HC1 = ZnCl 2 + 2H. 



The freed gas escapes through the delivery tube and 

 may be collected by downward displacement of water, 

 as was oxygen. 



The gas from the generator should be allowed to 

 escape until you feel sure that all the air that was in 

 the flask and tubes has escaped. Great care must be 



