CHAPTER XXVII. 



NON-METALLIC ELEMENTS. 

 OXYGEN SYMBOL ; ATOMIC WEIGHT 16 



OXYGEN is certainly the most abundant element in nature. It exists all 

 around us, and the animal and vegetable worlds are dependent upon it. It 

 constitutes in combination about one-half of the crust of the earth, and 

 composes eight-ninths of its weight of water. It is a gas without taste or 

 colour. Oxygen was discovered by Priestley and Scheele, in 1774, 

 independently of each other. 



Oxygen can be procured from the oxides of the metals, particularly 



Fig. 333. Oxygen from oxide of mercury. 



from gold, silver, and platinum. The noble metals are reducible from their 

 oxides by heat, and this fact assists us at once. If we heat chlorate of 

 potash, mixed with binoxide of manganese, in a retort in a furnace, the gas 

 will be given off. There are many other ways of obtaining oxygen, and 

 we illustrate two (figs. 333, 335). 



The red oxide of mercury will very readily evolve oxygen, and if 

 we heat a small quantity of the compound in a retort as per illustration 

 (fig- 333) we shall get the gas. In a basin of water we place a tube test- 

 glass, and the gas from the retort will pass over and collect in the test tube, 

 driving out the water. 



The other method mentioned above, viz., by heating chlorate of potash, 

 etc., in a furnace, is shown in the following illustration. Oxygen, as we 

 have said, is a colourless and inodorous gas, and for a long time it could not 

 be obtained in any other form ; but lately both oxygen and hydrogen have 



