3O ANSWERS TO PRACTICAL QUESTIONS 



4. Ought a faucet to extend into a barrel beyona the staves * 

 No ; because cross currents would be produced, which would 



interfere with the free passage of the liquid. 



5. What would be the effect if both the openings in one of 

 the arms in Barker's Mill were on the same side ? 



It would cease revolving. The pressure in each direction 

 would then be equal, and the arms would balance. 



PNEUMATICS. 



14. i. Why must we make two openings in a barrel of 

 fider when we tap it ? 



One to let out the cider, and one to admit the air. 



2. What is the weight of 10 cubic feet of air? 



100 cu. in. weigh 31 grs. ; hence 10 cu. ft. will weigh 31 grs. x 172.8 = .7652 

 Ibs. avoirdupois. 



3. What is the pressure of the air on one square rod of land? 



272/ 4 x 144 x 15 Ibs. = 588,060 Ibs. 



4. What is the pressure on a pair of Magdeburg hemispheres 

 4 in. in diameter, when the air is entirely exhausted ? 



3.1416 x 4 a x 15 IbP. = 753.9 Ibs. 



5. How high a column of water can the air sustain when 

 the barometric column stands at 28 in. ? 



28 in. x l3'/ a = 31 Vu feet. 



6. If we should add a pressure of two atmospheres, what 

 would be the bulk of 100 cu. in. of common air? 



The pressure is trebled, and according to Mariotte's law, the volume will 

 be reduced in the same proportion ; hence it will be 100 cu. in. -s- 3 = 33 1 /? 

 cu. in. 



7. If, while the water is running through the siphon, we 

 quickly lift the long arm, what will be the. effect on the water in 

 the siphon ? 



It will all run back through the short arm into the vessel. 



8. If we lift the entire siphon f 



The water will all run out the long arm. The reason of this 



