SOME PROPERTIES OF GASES 173 



two digits on either side of the hand of that dial. We 

 begin with the dial on the left and read toward the right, 

 writing only one digit for each dial. The numbers over 

 the dials mean that when the hand passes once around 

 the dial you will have used as many feet of gas as the 

 number over the dial indicates. If the number over 

 a dial is "10 thousand," the hand on that dial will measure 

 10,000 feet every time it goes once around, and as it 

 passes from one digit to another it measures 1,000 feet. 

 Read the gas meter in the illustration. 



QUESTIONS AND EXERCISES 



1. Explain how gases produce pressure. 



2. If we increase the pressure on confined gas, how will its 

 volume be affected ? 



3. The pressure in an automobile tire in a cool garage is 70 

 pounds; how will the pressure be affected if the automobile is 

 placed in the hot sunshine ? 



4. Why does the air escaping from a bicycle or automobile 

 tire feel cool? 



5. What practical use is made of the fact that gases take up 

 heat when they are allowed to expand ? 



6. Visit some artificial ice-plant and explain the process used. 



7. Give the origin of natural gas. How is artificial gas made ? 



8. Draw the dials and hands of your gas meter several days in 

 succession, also record the number of cubic feet. Do the same 

 for the electric meter. (Continue this until you know how to 

 read both of them.) 



