38 EXPERIMENTAL PLANT PHYSIOLOGY 



Fig. 17 



Experiment 19 



Aim. — To prepare and collect oxygen and to test its 

 properties. 



Method. — Fit a hard round-bottomed flask with 

 a cork and delivery-tube bent as in Fig. 17. Into 



the flask put about 

 20 grammes of a 

 mixture of three 

 parts of powdered 

 potassium chlorate 

 and one part of 

 manganese-dioxid e. 

 Clamp the flask 

 so that the end 

 of the delivery-tube 

 fits through a bee- 

 hive shelf standing in a pneumatic trough of water. 

 Gently heat the flask. 



As soon as the heating has been carried on long 

 enough to displace all the air in the flask, place an 

 inverted gas-jar full of water over the bee-hive shelf 

 and collect the gas that is coming off from the mixture 

 in the flask. A round glass plate must be used for 

 inverting the gas-jar. 



When the gas- jar is full of the gas, cover it under 

 water with a glass plate smeared with vaseline and re- 

 move it from the trough. Collect several jars in this 

 way. 



Before removing the flame disconnect the cork. 

 This is very important. If it is not done the water 

 will be drawn up the tube, as the gas in the flask con- 

 tracts, and the flask will then probably crack. 



Observations. — 1. The gas is invisible. It has no 

 colour or smell. 



2. It cannot be very soluble in water, because the 

 bubbles of the gas rose through the water and did not 

 seem to get any smaller. 



3. It is neutral to litmus. 



4. A lighted taper is put into a jar. It burns much 



