General Principles. 39 



To effect this, all that is necessary is to have a 

 tub or vessel of water, with a shelf in it, on which 

 a receiver may rest; a large tumbler will serve 

 for a receiver *. The tumbler must then be filled 

 with water, and be reversed with its brim under 

 water, and resting on the shelf. Put then some 

 of the red lead with a small quantity cf sulphuric 

 acid into a phial bottle in which is fixed air- 

 tight a bent tubef, which by an orifice in die 

 wooden shelf may communicate with the receiver 

 or tumbler f. Apply heat to the bottom of the 

 phial, (that of a wax-taper or common candle 

 will be sufficient) and after the common air 

 which the bottle contained is expelled, the oxygen 

 gas will rise in bubbles and fill the receiver or 

 tumbler, displacing the water as it enters. The 

 oxygen gas thus obtained is not the purest, for 

 it contains some carbonic acid gas, which, how- 

 ever, may be extracted by bringing the mouth 

 of the receiver in contact with some lime-water 

 in a bason, and slightly agitating it, when the 

 carbonic acid gas will be extracted by the attrac- 

 tion which the lime-water has for that substance. 

 Oxygen gas may be obtained in a still purer 

 state by heating a small portion of the black 

 oxide of manganese in a similar apparatus, only 

 that as a stronger heat is required, the vessel 

 containing the oxide should be of iron. 



PI. VI. fig. 19. 



f The tube may be inserted into the cork. 



J PI. VI. fig. 19. CDE. 



