OXYGEN. 9 



lightest of known bodies. This can be shown by 

 turning the mouth of a jar filled with it suddenly up- 

 ward, and at the same moment applying a taper. 

 There will be a slight explosion, and a body of flame 

 rising from the jar. On the other hand, if the jar be 

 gently lifted and the flame applied beneath, the burning 

 will be inside of the jar, and quite gradual. This 

 property may also be shown by filling a bladder with 

 the gas, and allowing it to rise. It is often used for 

 filling balloons, its lightness giving them very great 

 buoyancy. 



4. Mixed with common air, this gas is dangerously 

 explosive. The first portions which pass over from 

 the bottle are therefore to be rejected; and a match 

 ought never to be applied to a jar or bottle containing 

 it, or in which it is being made, without having first 

 tested the purity of a small quantity collected in a little 

 tube. If this burns quietly when a taper is placed 

 beneath its mouth, the gas is sufficiently pure to use 

 with safety. 



5. This gas can be breathed without very injurious 

 effects, but it will not sustain life. In an atmosphere 

 of pure hydrogen, every animal would soon die. 



The next of these three gases is one of exceeding 

 importance : its name is Oxygen. It is colorless, 

 tasteless and inodorous, like hydrogen, that is, when 

 pure: as ordinarily made, it has some impurities. 

 The easiest way of preparing it is to mingle some 

 chlorate of potash with a small portion of the black 

 oxide of manganese. Both of these substances can be 

 procured at the shops in our cities and large towns. 

 Half a teacupful of the mixture will produce quite 

 enough gas for ordinary experimental purposes. The 

 chlorate of potash should be powdered and dried, be- 

 fore mixing with the manganese. When a>l is ready, 

 the mixture is to be put into a flask with a thin bot- 



