PAPERS OX CHEMISTRY AND PHYSICS 245 



and where possible, dissectable commercial appliances 

 commonly used in the life of every community. TVhat are 

 a few of these commercial appliances? Cistern jDnmps, 

 coal stoves, gas stoves, electric stoves, meters of every 

 kind (gas, water and electric), water and electric motors, 

 gasoline, gas and hot-air motors, pressure cookers, heat 

 regulators, electrical transformers, rectifiers for chang- 

 ing ordinary 110 volt A. C. to low voltage D. C, ice and 

 mechanical refrigerators, cameras, telescopes, opera 

 glasses, transformers and X-ray outfits, some musical in- 

 struments, blood-pressure apparatus and such other ap- 

 pliances as involve jDhysical principles and are suitable 

 and available. The list should include eventually practi- 

 cally eveiy appliance which is not too large or costly 

 which is found in the community. 



If some of our laboratory periods are to be spent in 

 experimentally answering practical questions which arise 

 in the class recitation and not to be found in text or manu- 

 al, how much will our ordinary laboratory methods be 

 modified? Suppose that the following question has been 

 raised in the class during the discussion of why electricity 

 has not so completely displaced gas in cooking and heat- 

 ing as it has in lighting: What is the relative cost and 

 time required to raise a quart of water from tap tempera- 

 ture to the boiling point, first, by using a gas stove or hot- 

 plate and, second, by using an electric stove or hotplate ? 

 It is then the teacher 's duty to plan an exercise which wiU 

 answer the question. In my judgment it is neither feas- 

 ible nor desirable that high school students make such in- 

 vestigations individually. Class or group work is en- 

 tirely sufficient. This does not mean that the teacher 

 should give this rather lengthy exercise as a clear-cut 

 demonstration while the class looks on. If the group 

 consists of no more than 10 to 15 students the teacher can 

 stand aside and assign the duty of making the proper con- 

 nections to certain students. Other students may be as- 

 signed the task of inspecting those comiections. Still 

 other students may later be assigned the duty of read- 

 ing the meters and taking the temperature and time. 



To conduct such a group experiment, perfect order and 

 careful attention must be required of every student. 



