36 ANSWERS TO PRACTICAL QUESTIONS 



1467. If 9 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 ? If we lift the entire siphon ? 



The question assumes the siphon to be flexible. If the bot- 

 tom of the long arm be below that of the short arm, the water 

 flows through it toward the lower level. By lifting it the rate 

 of flow diminishes until its level is the same as that of tho 

 short arm. On lifting it still higher, the water contained in the 

 siphon flows back through the short arm, and the siphon is 

 thus emptied. If, however, the whole siphon is lifted, it is 

 emptied through the long arm. 



8. WJien the mercury stands at 29\ in. in the barome- 

 ter, how high above the surface of the ivater can ive place 

 the lower pump-valve ? 



In theory, 29^ in. x 13 = 398} in.; in practice, the distance 

 is much less than this. 



9. Can we raise water to a higher level by means of a 

 siphon ? 



There is no power in a siphon ; it is only a way of guiding 

 the flow of water to a lower level. 



10. If the air in the chamber of a fire-engine be con- 

 densed to T V its former bulk, what will be the pressure due 

 to the expansive force of the air on every square inch of 

 the air-chamber ? Ans. 24O Ibs. 



11. IVtiat causes the bubbles to rise to the surface when 

 we put a lump of loaf-sugar in hot tea ? 



The bubbles of air contained in the pores of the sugar rise 

 because they are lighter than the water. 



12. When will a balloon stop rising ? IVJiat weight can 

 it lift ? 



It will stop rising when the weight of the balloon and its 

 contents is just equal to that of the same volume of rarefied 

 air which it displaces. It can lift a weight equal to the dif- 

 ference between the weight of the hydrogen or coal gas with 

 which it is filled and that of the air in which it is immersed, 

 minus the weight of the balloon itself. 



