80 HEAT. 



were used, it would be found that the level 

 of the water inside, would never be more than 

 thirty- three feet above the level outside. The 

 remainder of the tube wonld be empty, as re- 

 presented in the figure. In other words, the 

 pressure of the atmosphere will sustain a col- 

 umn of water thirty-three feet high. Water 

 rises in a pump from this cause. 



189. QUANTITY OF MERCURY THE 



incheTofnier- PRESSURE OF THE AIR CAN SUSTAIN. 



cury will the i n performing the experiment of 



air sustain? 



the last paragraph with mercury, it 

 will be found that the level within the tube, will 

 be thirty inches above the external level. In other 

 words, the pressure of the atmosphere will sustain a 

 column of mercury thirty inches high. 



190. If a long tube is used, there is, of 



Explain the __ . . 



Toricdlian course, an empty space above. This is 

 vacuum. ca ii e d the Toricellian vacuum, from the 



fact that a vacuum was first produced in this manner by 

 an Italian philosopher, named Toricelli. It is not an 

 absolute vacuum, a small portion of mercury being al- 

 ways present in the space in the form of transparent 

 vapor. 



191. BOILING. Thus far we have con- 



Whatismeant ,-,,,,,, . /, f 



by the term sidered solely the formation of vapors from 

 boiling? the surfaces of liquids< But where any 



liquid is heated up to a certain point, vapor forms in 

 bubbles below its surface. The production of vapor 

 with ebullition is called boiling. 



