28 Introduction. 



pounds per minute, equal to 16.5 foot-tons in the same 

 time. To raise grain in an elevator to a hight of 20 feet 

 at the rate of 16.5 tons per minute would require 20 horse- 

 power. 



If a horse is walking 2.5 miles per hour and exerting a 

 steady pull on his traces of 100 pounds then the effective 

 energy he is developing is 



100X5,280X2.5 _ 

 60X60X550 



and this for a well fed horse weighing 1,000 pounds, work- 

 ing 10 hours per day at the rate of 2.5 miles per hour, is 

 called a fair day's work. If a 1,500-pound horse could 

 do work in proportion to his weight then his ability to de- 

 velop energy would be equal to the standard English horse- 

 power of 550 foot-pounds per second. Gen. Morin, how- 

 ever, has placed the ability of the average horse to do work 

 at the rate of 435.8 foot-pounds per second. 



38. Heat Unit. In the steam engine the energy of heat 

 is converted into work, and since heat is a form of molecu- 

 lar motion its quantity must have a fixed relation to the 

 temperature of a given amount of material. The English 

 and American heat unit is the amount of heat energy which 

 is required to raise the temperature of one pound of pure 

 water from 32 F. to 33 F., and since one form of energy 

 may be converted into another the value of a heat unit may 

 be expressed in foot-pounds. The English scientist, Joule, 

 was the first to measure the number of foot-pounds of work 

 which one heat unit could do and found it to be 772, which 

 when corrected for the mercurial thermometer became at 

 15 C. 775 foot-pounds. Kowland obtained the value 778.3 

 foot-pounds. This means that the source of heat which is 

 able to raise the temperature of one pound of water one 

 degree every second would also be able to raise 778.3 

 pounds one foot high in the same time. 



39. Determination of the Mechanical Equivalent of Heat. 

 In order to ascertain the value of the heat unit in foot- 



