90 APPENDIX. 



11. Let the tOiiehcr explain the meaning of oxidation. 

 When oxygon unites with metals, they form new sub- 

 stances, unlike the metal from which they were formed. 

 Put a little red lead (oxide of lead) into the bowl of a 

 tobacco-pipe, filled with finely-pulverized charcoal ; 

 then let the pipe-head become red-hot, by placing it in 

 the fire, or in the frame of a spirit-lamp. The oxygen 

 combined with the lead will have united with some 

 of the charco.il, forming carbonic acid gas, and the 

 lead will be foand again reduced to the metallic state. 



Next put a little of the red oxide of mercury into a 

 small retort, and apply a spirit-lamp (see Fig. 8). The 

 oxygen will be driven off by the heat, and the bright 

 fluid metal, mercury, may be collected, as it trickles 

 down the beak of the retort. 



12. Put a little black oxide of manganese into a Flor- 

 ence flask, and pour upon it a portion of muriatic acid, 

 then apply the heat of a small lamp. The chlorine will 

 be set free, and may be collected in bottles filled with hot 

 water, as seen in Fig. 8. It cannot be collected over 

 cold water, because cold water rapidly absorbs the gas. 

 Chlorine being heavier than the atmosphere, it may be 

 collected in bottles filled only with common air, by at- 

 taching the India-rubber tube to the neck of the flask, 

 and allowing it to reach the bottom of the bottle to be 

 filled. It will thus gradually force the air out of the 

 bottle, a-nd occupy its place. Be careful not to inhale 

 the gas ; and experiments with chlorine should be per- 

 formed under an open window, or in the open air. Put 

 a taper into a bottle of chlorine ; it is instantly extin- 



