CHAPTER XII 



NON-LIVING THINGS 



In the lower grades evaporation may be presented very 

 simply. Take plenty of time to prove that, while some of 



the water that disappears after a rain is 

 Evaporation 



absorbed into the ground, much of it passes 

 into the air as invisible water vapor. Show that water in 

 closed vessels will remain indefinitely, while that in open 

 vessels is soon taken away by the air. Boiling a small 

 quantity of water shows that heat hastens evaporation. 



For grades above the first two, the experiments may be 

 extended to the evaporation of volatile liquids, such as 

 alcohol, gasoline, ether, chloroform, carbon-bisulphide, 

 cologne, and many others. Only a teaspoonful or two 

 should be used of those substances which vaporize rapidly 

 into highly inflammable gases. Pour into the hollow of 

 a pupil's hand a small amount of one of the liquids men- 

 tioned, and caution him not to spill it. The liquid soon 

 disappears ; if it has a strong odor it can be smelled through- 

 out the room, so helping tell the story of its diffusion 

 through the air. 



' Next make a series to test the comparative rapidity of 

 the evaporation of several liquids. Arrange small, shallow 

 dishes with labels showing what each one is to contain. 

 The following liquids may be used, glycerine, water, coal 

 oil, turpentine, alcohol, gasoline, carbon-bisulphide, and 

 chloroform. Use equal amounts of these substances, and 



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