shine] ELEMENTARY SCIENCE 277 



EXPERIMENT EIGHT 



This was an experiment to show that some metals are better 

 than others for the conduction of heat. We preceded it by fram- 

 ing a definition of heat and by studying both the Fahrenheit and 

 Centigrade thermometers. By very simple experiments we stud- 

 ied eight sources of heat: frictional, solar, terrestial, chemical, 

 electrical and animal heat. We showed that percussion and com- 

 bustion produced heat by hammering a wire and by lighting a 

 candle. 



In this experiment we used some sealing wax, ten marbles, a 

 Bunsen burner, and a copper and iron wire. The wires were about 

 one-eighth of an inch in diameter and a foot long. By means of 

 the sealing wax we fastened five marbles to each of the rods. The 

 first marble was placed two inches from the end, and the others 

 were an inch apart. Then the rods were crossed and the two ends 

 were held in the Bunsen flame. The heat, traveling by radiation, 

 caused the two nearest marbles to drop off — one on each rod. 

 Then as the heat traveled along the copper rod the wax slowly 

 melted, and one by one, all five of the marbles on the copper wire 

 dropped off. Only one marble dropped fron the iron rod. Thus 

 the class concluded that copper was a better conductor of heat 

 than iron. I explained that copper was used in electrical wiring 

 because it was the best and cheapest for the conduction of elec- 

 tricity. 



I departed from the experiment to say that air was a poor con- 

 ductor of heat or cold and explained thus why feathers, furs, flan- 

 nels, and even a blanket of snow are so warm. If a Thermos bot- 

 tle is procurable, one can readily explain, at this point, that a 

 vacuum (if perfect) will not conduct either heat or cold. 



EXPERIMENT NINE 



We sought to show by this experiment that heat is taken in 

 whenever snow or ice melts. The class knew and were told noth- 

 ing of latent heat. We used a tin cup filled with snow and a board 

 partly covered with water. We placed the tin cup in the water 

 and scattered common table salt (rock salt would be better) on 

 the snow in the cup. Within ten minutes, although the room was 

 warm, the cup was frozen to the board. The sides of the cup were 

 covered with a light frost, and we sought the explanation for that, 

 too. 



