82 FIRST YEAR COURSE IN GENERAL SCIENCE 



Passenger elevators are constructed with a strong cage or 

 frame-work above the platform. When the operator stops 

 the elevator, he closes a valve so as to prevent more water 

 coming into the cylinder. When the 'elevator descends, he 

 opens a valve and allows water to escape from the cylinder; 



FIG. 34.- A HYDRAULIC PRESS 



1. By means of a small pump p, water is forced from i through t, into 

 the cylinder i'. The pressure exerted by one square inch of the surface 

 of the piston p is transmitted to each square inch of the surface of p' '. If the 

 pressure of p is 25 Ib. and p f is 100 times the area of p, what is the pres- 

 sure upon p r ? 2. Why does not p' sink back after being pushed up? In a 

 passenger elevator, the valves V and V are opened or closed by the operator 

 in the elevator. 3. Learn from a dictionary the meaning of hydraulic. 



the elevator then descends by gravity, checked by the resist- 

 ance of the water as it moves slowly out of the cylinder. 



88. Solution. Liquids have the power of dissolving 

 other substances, that is, of absorbing particles of other 

 substances between their molecules. The absorbed solid, 

 liquid, or gas disappears and the result is a liquid mixture 

 called a solution. The solution may have a different taste, 

 odor, or color from the original liquid, which is known as 



