160 



CHEMISTRY. 



heat the contents of the flask, and yellowish-green vapors 

 of chlorine will arise and pass over into the jar arranged to 

 collect it. 



The reaction which takes place is somewhat complex, but 

 you will understand it by studying this equation: 



Sodi Sulphuric ^anpi. Hydro-sodium w Chlo- 



dioxide. chlorlde ' acl(L sulphate. sulphate. ' ter - r ine. 



MnO a + 2NaCl + 3H 2 SO 4 = MnSO 4 + 2(NaIISOJ + 2H a O + C1 2 



The manganese dioxide is necessary to furnish oxygen to 

 unite with the hydrogen of the sulphuric acid, forming wa- 

 ter. What happens when we omit the addition of manga- 

 nese dioxide you will see very soon. 



211. Another "Way of Obtaining Chlorine. Chlorine gas 

 may also be obtained by heating hydrochloric acid with 

 manganese dioxide. The heat required is not high plac- 

 ing the flask in a bowl of hot water is sufficient. If the 

 gas stops coming over, add more hydrochloric acid, for this 

 is the source of the chlorine. 



As the gas is about two and a half times as heavy as air, 



it can be collect- 

 ed in ajar, as rep- 

 resented in Fig. 

 66, the lighter 

 air being driven 

 out to give place 

 to it. The ex- 

 planation of the 

 chemical change 

 in the flask is 

 this: There is a 

 large amount of 

 oxygen in the ox- 

 ide of manganese, 

 which is therefore loosely attached to the metal, and ready 



Fig. CO. 



