20 



CHEMISTRY FOR AGRICULTURAL STUDENTS 



metals in air. Should one or more of these oxides yield up 

 their oxygen, or a portion of it, on heating to a high tempera- 

 ture, a method will have been found of preparing the oxygen 

 gas of the air in a pure state. A smouldering splint will 

 indicate whether the gas is being evolved. 



Heat some red lead or red oxide of mercury in a hard glass 

 tube, fitted with a cork and bent tube, as shown in Fig. 6, 

 supported on the ring of a retort stand, and collect the gas 



evolved by allowing it to bubble 

 up into an inverted test-tube or 

 cylinder filled with water. When 

 all the water has been displaced, 

 and the tube is full of gas, place 

 the thumb or a glass plate over 

 the orifice while still under 

 water; then turn up and ex- 

 amine the properties of the gas. 

 In taste, odour, and colour it 

 would be expected to be indis- 

 tinguishable from air, air being tasteless, odourless, and 

 colourless, but, being the pure active constituent, it should 

 support combustion more readily. Try with a taper and a 

 smouldering splint. 



Fill a bottle with oxygen (supplied) by water displacement, 

 and having placed a bit of phosphorus in a deflagrating spoon, 

 and set fire to it, plunge it into the bottle. Repeat the experi- 

 ment, using sulphur instead of phosphorus. Then 

 try a lump of charcoal supported by a copper 

 wire passing through the brass plate of the spoon. 

 Finally, try a steel watch spring, to the end of 

 which a bit of taper is fixed to serve as a fuse, the 

 other end of the spring passing through the brass 

 plate. Observe in each case that the oxygen is 

 more active as a supporter of combustion than 

 Fig. 7. air, but that the product of combustion is the 



Fig. 6. 



