MATERIALS WHICH PL.VNTS DERIVE FROM THE Alli. 



23 



and examine its remarkable properties. In the air its 

 amount is so small that its properties are not so striking. 



examination, if we close it securely with a cork dexterously inserted, 

 without raising its mouth above the surface of the water in the basin. 

 A common wash-hand basin may be used for collecting gas; but a 

 small trough fonned of tin-plate, and provided with a shelf pierced witli 

 two or three holes, termed a pneumatic trough, is usually employed. 

 Water is poured into this trough until it rises about an inch above the 

 surface of the shelf, and when it is desired to collect the gas, a bottle full 

 of water is placed with its mouth directly over one of the small holes, 

 and under the same hole the tube from which tlie gas escapes is placed. 

 The directions which we are about to give for the preparation of 

 oxygen will now be understood without difficulty. Oxygen gas is one 

 of the most extensively diiFused bodies in nature, forming about a half 

 of the crust of the earth, and being an essential ingredient of water and 

 of the bodies of plants and animals. It is never met with, except in 

 combination with other bodies, and the usual method of procuring it in 

 a separate state is to apply a strong heat to certain substances which 

 contain it in large quantity. Thus, by placing in a retort, or Florence 

 flask fitted with a cork, through which a bent tin or glass tube passes, 

 a mixture of two parts of Chlorate of Potash, with one part of black 

 oxide of Manganese (49), both substances being previously rubbed to 

 tuie [Kjwder in a mortar, and applying heat to the vessel by means of a 

 spirit lamp, the tube of the retort, or that attached to the flask, being placed 

 as described imder the mouth of a bottle inverted and full of water, the 

 gas will escape tlirough the tube, and expel the water from the bottlt. 

 The engraving will show the arrangement of the apparatus required. 



Ulustration of the properties 

 of Oxygen, 

 a. A tube may be filled 

 with the gas, which will be 

 found to possess neither co- 

 lour, smell, nor taste. 6. 

 Into another tube filled ^-ith 

 gas, and removed from the 

 trough, by placing the thumb 

 underwater over its mouth, 

 a bit of taper, with its flame 

 just extinguished, may be 



t'ig. I. 



introduced; the flame will immediately be rekindled, and burn witli in- 

 creased brilliancy, but the gas will not itself take fire. It is a supporter 

 of combustion, but not itself combustible. 



c. A piece of pliosphorus about the size of a small 

 pea, place<l upon the iron spoon, may be ignited by touch- 

 ing it with a piece of lighted wood, and immediately in- 

 tnxiuced into a half-pint bottle of the gas. It will burn 

 with a dazzling white light. When the quantity of oxy- 

 gen in the atmospheric air is diminished 8 per cent, 

 (Liebig), the latter becomes injurious to animal life, and 

 incapable of supporting -'..MiJ.ii^tion. 



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