PRESSURE OF WATER AND OF AIR 



17 



FIG. 9. 



the medicine dropper under the mercury, pinch the bulb so as 

 to expel the air as completely as possible, and then release it. 

 Does the bulb expand completely? Why? 



d. Siphon. Put the shorter arm of the bent tube (Fig. 9; 

 make this, if necessary, as in 4 of the Introduction) into a 

 vessel of clean water, and suck the 

 air out of the longer arm. What 

 happens? Continue removing the 

 air until the longer arm is full of 

 water; then remove your mouth, and 

 note what .happens. Place an empty 

 vessel under the longer arm. Have 

 the top of the second vessel slightly . 

 higher than the bottom of the first 

 one. How long does the water run? The bent tube with the 

 water flowing through it is a siphon. How far above the 

 water level of the first vessel may the bend of the siphon be? 

 What pushes the water up to the bend of the siphon? What 

 pulls it down in the longer arm? 



Pour the water back into the higher vessel, and fill the siphon 

 with water by immersing it in a pail of water or by holding it 

 under a faucet of running water. Close the opening of the 

 longer arm with your finger, and put the shorter arm into the 

 higher vessel; then remove your finger, and note the result. 



For what purposes may a siphon be used? 



EXERCISE 13 

 PRESSURE OF WATER AND OF AIR 



Apparatus and Materials. Deep glass vessel, small glass vial, wire, 

 and stick (or glass tube); wide-mouth bottle, two-hole stopper (one 

 hole plugged), bent glass tube. 



a. Fill with water the deepest glass dish you can find. A 



