Page:Popular Science Monthly Volume 21.djvu/232

222 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 experimenting 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 plaster 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 subject is presented becomes important. It is of the highest consequence that the more dependent parts of the science should not be put forward 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 hydrogen 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