222 THE POPULAR SCIENCE MONTHLY. 



If, after this, we decompose water by a battery, the students will 

 at once recognize the process for themselves as decomposition ; and it 

 confirms their previous analysis of water. But, if I begin experiment- 

 in cr by battery decomposition, they can not study out for themselves 

 the rationale of the process. Of course, the teacher can explain and 

 point out and make it understood, but they take it all pretty much 

 upon authority, and their minds are far less active and independent. 

 And so, of making oxygen at first with potassium chlorate. The 

 chlorate is a less simple substance than the red oxide of mercury ; 

 and the presence of the binoxide of manganese, with the catalysis, 

 complicates the process. 



While directing this experimental study I do not tell them any of 

 the facts which come on testimony, unless, like the fact about the 

 making of the red oxide of mercury, it is a necessary step in some 

 chain of reasoning which they can make out mainly for themselves. 



The precautions necessary in using such substances as sodium make 

 it unwise and imprudent to set careless young folks to handling them. 

 One accident would bring lasting disrepute on our chemical study. 



Showy experiments are demoralizing, though they excite for the 

 time a sensational interest. But, when young folks really think for 

 themselves, they are so pleased with it that they can take the highest 

 interest in a very simple process. There is an experiment which I 

 learned from that capital book, "Eliot and Storer's Chemistry," which 

 illustrates a good many things I have said. It is designed to show the 

 great diffusibility of hydrogen. A tube, closed at one end with plas- 

 ter of Paris, is filled with hydrogen, and put in a tumbler of water for 

 a day or two. The water first rises in the tube, then sinks to the level 

 of that in the tumbler, in consequence of hydrogen escaping faster 

 than air comes in. When I first taught chemistry, my pupils took no 

 interest in this experiment. When I tried making them discuss the 

 changes, and discover for themselves the property of hydrogen which 

 causes them (which they do with all ease), they find it more interesting 

 than the burning of phosphorus in oxygen. This experiment shows, 

 too, how genuine inductive teaching must necessarily be oral teaching, 

 for a text-book merely tells the philosophy of the changes, which is 

 precisely the thing the pupils ought not to be told. 



When chemistry is taught inductively, the order in which the sub- 

 ject is presented becomes important. It is of the highest consequence 

 that the more' dependent parts of the science should not be put for- 

 ward in the beginning. I do not think the order of our American 

 text-books so good as that of Stockhardt. 



I will state, in a very few words, the order which seems to me best. 

 I usually make the pupil study, first, the individual properties of the 

 thirty chief elements, taking up no compounds but oxides and hydro- 

 gen acids. The pupil should test the oxides with red or blue litmus ; 

 note the acid or basic taste ; note which are insoluble in water. The 



