NOTE ON OXYGEN DEMONSTRATIONS JOSEPH I. OSER Simon Gratz High School, Philadelphia, Pennsylvania
T
HE TEACHER of chemistry has a t his command, in the lecture demonstration, a powerful instrument which must be used with restraint. Long before the present pother about visual education, the chemistry teacher employed this most direct means of instruction. He has been warned not to abuse it. "The noise of an explosion may drive the principle of the experiment out of the student's head," was the way this warning was phrased by an experienced teacher. The drama of the experiment must he subordinated to its pedagogy. However, it is occasionally difficult to resist the temptation! In preparing a recent talk for the school assembly it
proved "good theater" to overemphasize a certain group of experiments. In demonstrating the ability of oxygen to support combustion, it was found that the beauty of the experiments can he much enhanced by performingthem in almost total darkness. In the daytime, in auditorium or classroom, the same arrangements to exclude light should he made as are necessary for projecting picturesblack shades are best. In the evening school it is merely necessary to turn off the lights. A small yellow Bunsen flame or a candle will furnish sufficient illumination for the experimenter. The beautiful appearance of the combustions in oxygen, in the dark, will prove a revelation. The sparkling of iron, the bright yellow glow of charcoal, the white glare of magnesium, the yellow hlaze of phosphorus, the eerie purple flame of s u l f u r a l l assume a new and strange beauty in the absence of competing light.
