INTERESTING THINGS ABOUT THE AIR 



5. Measuring air pressure in tires. In order to secure the 

 proper air pressure in an automobile tire and at the same 

 time to avoid danger of bursting it, 

 there is need for a means of measur- 

 ing the pressure and also need for 

 knowledge of the amount of pressure 

 which will make the tire give the 

 best service. Pressure gauges (fig. 4) 

 as measuring devices are in common 

 use. Various types of these gauges 

 are manufactured for a variety of 

 different purposes. 



Since the best service is secured 

 by using them at the proper air pres- 

 sure, it is now customary to take 

 the tire manufacturers' recommenda- 

 tions on this point, and these may 

 be secured from the salesman. The 



Gauge, opened to 

 thoic interior 



Rubber toe, held by 

 spring, tchich expands 

 under pressure and 

 forces up the gautie 



4. Air-pressure gauge 



By attaching this gauge to the 

 Weight of the machine and load to air tube of an automobile or 



be carried are considered in estimat- bi<> >' cle tire ''"* " f f r 



pressure may be measured 



ing the pressure, as is shown in the 



following table, which gives the pressures recommended for 



some of the commonly used kinds of tires: 



6. Working under water. In laying the foundations of 

 bridge piers and other structures which must rest below 

 water level (fig. 5), it is common for the laborers to work 

 in a large steel chamber which has no floor and which rests 

 upon the bottom of the lake or river. This is called a caisson. 



