CHEMISTRY IN HIGH-SCHOOLS. 219 



chemistry. But it is not all that is needed. Mental activity is the 

 important thing. 



I will illustrate the plan which has proved best in my own experi- 

 ence, merely saying, first, that even where pupils have studied physics, 

 I have a preliminary drill to make sure the girls are quite clear about 

 the forms of matter, the properties of liquids and gases, attractive and 

 repulsive forces. I do not say a word to them about chemical attrac- 

 tion, because I wish them to study that out for themselves. Some- 

 times they have already learned by heart a definition from some book 

 on physics ; but, as Thomas Carlyle would say, " by the blessing of 

 Heaven they have generally forgotten it." 



I think the best experiment to begin with is the evolution of oxy- 

 gen gas by heating the red oxide of mercury. This is not the easiest 

 or the most convenient way of obtaining oxygen, but it is much the 

 simplest process.* I do not usually tell my pupils anything not 

 even what the substance is which they are to make ; but they know 

 I shall question them closely about what they have seen. When the 

 experiment is concluded the gas tested with a glowing taper ; the 

 residue of mercury examined ; and a little of the red oxide put into 

 water and stirred, to show that it will not dissolve I usually ask 

 questions about as follows : 



" When the jar was lifted from the water to the shelf, why did 

 not the water fall out ? Why did the water afterward sink in the 

 jar ? Did you see anything in the jar as the water fell ? Why do 

 you think there was anything in the upper part of the jar ? What 

 form of matter was it ? How do you know that it was not air ? How 

 was it like air? How was it unlike air ? Had it color or smell ? Did 

 it burn ? What was it burned ? Did the gas have anything to do 

 with the burning ? " f I then tell them the gas is called oxygen ; and 

 I write on my blackboard the name and symbol, with a list of the 

 properties which they have just discovered. 



I then proceed to ask : " What remained in the ignition tube at 

 the close of the experiment ? What form of matter was it ? Did 

 you ever before see anything with that shiny luster ? What class of 

 bodies have it ? " Then I tell those who do not already know that it 

 is mercury, and I give the symbol, Hg. 



I then say : " Where were the gas and the liquid when that red 

 powder was placed in the tube ? What became of the powder ? Did 

 it take any force to separate the gas and liquid which you say formed 

 the powder? What was the force? What sort of a force is heat? 

 Do you suppose any force held the oxygen and mercury togeth- 

 er ? Do you know a general name given to forces which unite 



* I always, of course, have ready a quantity previously otherwise made. 



f I find that pupils will at first, of themselves, make the somewhat conventional dis- 

 tinction between " combustibles " and " supporters of combustion." For a while I let 

 this pass. 



