ATMOSPHERIC PRESSURE 43 



The self-starting device is shown in Fig. 34, and consists of a bulb 

 (4) sealed into the lower end of the tube (2) and an inner tube (5) 

 sealed into the base of -the bulb and reaching into the opening of the 

 bulb at the top. Here the end is somewhat constricted, and its 

 size and position with respect to the top of the bulb are so adjusted 

 that an " air trap " is produced at (6). A small opening (7) is 

 made at the lower part of the bulb. 



If the bulb be placed at a considerable depth in the liquid to be 

 siphoned, the liquid flows into the bulb through (7) and displaces 

 the air, which, with the water passing through the inner tube (5) , 

 rises in a broken column in tube (2) and flows out through the deliv- 

 ery tube. 



The wide application of the self-starting siphon is apparent 

 especially in chemical laboratories, drug stores, manufacturing and 

 other establishments where liquids and various solutions are in 

 constant use. In transferring corrosive poisons or valuable liquids 

 it obviates accident or waste. 



Air Has Weight. Place on each end of a stick a flask closed by a rubber 

 stopper, and balance the stick carefully. Remove the stopper from one of 

 the flasks and heat the flask. 



The air will expand and some of it will come out. Replace the 

 stopper. The stick will no longer balance. The air in the heated 

 flask does not weigh as much as before. Air has weight. 



Another interesting way to show that air has weight is to balance an old 

 electric light bulb on a stick. Remove the bulb and with a blow pipe blow a 



LIGHT BULBS 



FIG. 36. Balance two electric light bulbs on a stick. With a blow-pipe and 

 flame carefully make a hole in one. Why will they no longer balance? A 

 nitrogen-filled bulb should not be used. Why? 



