134 EXAMPLES. 



ume, and the temperature changed to f, find the pressure 

 P' on the piston. , __ I + at' 



I + at 



18. If a cubic foot of gas, whose temperature is 100 and 

 elastic force 29 inches, be cooled down to 40, and com- 

 pressed by a force equivalent to 10$ inches, find its volume. 



Ans. 4334.7 cubic inches. 



19. If 20 cubic inches of air, whose temperature is 56 

 and elastic force 28.8 inches, be expanded to 25 inches by 

 the application of heat, and if the elastic force become 31 

 inches, find the temperature. Ans. 234.27. 



20. Let 100 cubic inches of air have a temperature 32 

 and a pressure 29.922 inches; if the temperature become 

 60, and the pressure 30 inches, find the volume. 



Ans. 105.42 cubic inches. 



21. A cubic foot of air at a temperature of 100, and 

 under a pressure of 29 inches of mercury, is cooled down 

 to 40 and compressed by an additional 10 inches of mer- 

 cury. Find the volume. Ans. 1137.86 cubic inches. 



22. If h and h' be the heights of the surface of the mer- 

 cury in the tube of a barometer above the surface of mercury 

 in the cistern at two different times, compare the densities 

 of the air at those times, the temperature being supposed 

 unaltered. Ans. h : h'. 



23. A conical wine-glass is immersed, mouth downwards, 

 in water. How far must it be depressed in order that the 

 water within the glass may rise half-way up it ? 



Ans. 7//, where // is the height of the water barometer. 



24. A cubic foot of air having a pressure of 15 Ibs. on a 

 square inch is mixed with a cubic inch of compressed air, 

 having a pressure of 60 Ibs. on a square inch. Find the 

 pressure of the mixture when its volume is 1729 cubic 

 inches. Am. 



