64 



Introduction to the Study of Science 



length of glass tubing of very small diameter. Put the end of the 

 glass tubing into some water so that a drop becomes inclosed in the 

 tube. Cool the flask by wrapping it in a cloth wrung out of cold 

 water. In which direction does the drop of water move? Remove 

 the cold cloth and warm the flask with the hands. Note the direction 

 of movement of the water. Does warming increase or decrease the 

 volume of the inclosed air ? What is the effect of cooling ? 



A similar experiment will illustrate a change in the weight of a 

 unit volume of air. Put the end of the tubing into water in a beaker, 



as in Fig. 18, and heat the flask. 

 What does the escape of bubbles 

 of air mean? Does the air re- 

 maining in the flask weigh as 

 much as the original air con- 

 tent? With this fact in mind, 

 do you think that a cubic inch 

 of cold air weighs the same as a 

 cubic inch of warm air? Will 

 it weigh more or less ? Explain 

 now the circulation of air in the 

 box-and-candle experiment. 



Explain why a tire tube in- 

 flated with cold air may " blow 

 out " when heated. To what 

 may the heating be due ? Will 

 a basket ball, partly filled with 

 cold air and then warmed so 

 that it becomes tight, weigh 

 more after heating than be- 

 fore? Explain your answer. 



These facts are fundamental 

 not only in the case of the problem in hand, but with the larger air cur- 

 rents, such as local winds, planetary winds, and zones of temperature. 



Repeat the experiment of air expansion under changes of tempera- 

 ture with some other gas, such as illuminating gas. You will find 

 that it behaves exactly as air does under similar conditions. 



FIG. 18. The volume of air changes 

 with changes in temperature. Explain 

 how this device illustrates the fact stated. 



The general law. A long series of experiments with gases 

 has made it possible for scientists to formulate the general law 

 that all gases expand with the rise of temperature and contract 

 with the fall of temperature. 



