80 



GENERAL SCIENCE 



FIG. 80. Siphon. 



docks below the water level, it is quite 

 common for the laborers to work in a 

 large steel chamber called a caisson. 

 The water is kept out of the caisson 

 by air, which is forced into it by pumps 

 with sufficient pressure to overcome the 

 pressure of the water outside. In the 

 more complex caissons, the entrance and 

 .exit of the workmen without allowing 

 the air to escape from the caisson is 

 made possible by means of air locks 

 which work on the same principle as the 

 water locks of a canal. Compressed air 

 can do work in various ways. The sand 

 blast, the air brake, the pneumatic 

 hammer, and the diving bell (Figure 82) 

 are illustrations of many uses. 



the side of the tumbler. Can 

 you explain the action of the 

 water in this experiment ? 



Experiment 18. Fit a flask with 

 a two-hole rubber stopper and ar- 

 range glass tubing as shown in 

 Figure 81. The shorter tube should 

 terminate in a much smaller bore 

 inside the flask, while the longer 

 tube should just reach the stopper. 

 A little water must be placed in the 

 flask to start the siphon. How does 

 this differ from the siphon in the 

 previous experiment? What deter- 

 mines the force of water in the jet? 



Compressed Air. In laying 

 the foundations of piers and 



FIG. 81. Another 

 Form of Siphon. 



