88 SCIENCE OF THRESHING. 



become appreciable and that they are capable of 

 doing work of a kind that can be used. 



Now if the heat given to water when it is turned 

 into steam is capable of making the steam do work, 

 there must be a certain quantity of heat which will 

 do a certain amount of work. The standard by 

 which we measure heat is known as the British Ther- 

 mal Unit; or, as commonly abbreviated, the B. T. 

 U. This is the quantity of heat which is required to 

 raise one pound of water one degree in temperature. 

 Careful experiment has demonstrated that you must 

 impart at least one B. T. U. of heat to water after 

 the 212 mark is passed to enable the steam to lift one 

 Ib. in weight 778 ft., or 10 Ibs. in weight 77.8 ft., or 

 100 Ibs. in weight 7.78 ft. In other words, one B. T. 

 U. is equivalent to 778 foot-pounds, and you thus 

 have the energy which is expended by the vibrating, 

 moving molecules of the water to which heat has 

 been applied, measured by something which all can 

 understand, and which is the common term to denote 

 the pull required on the driving belt of the separator. 



It has been found that the burning of one pound 

 of coal gives out sufficient heat to raise the tempera- 

 ture of 14,000 Ibs. of water from 62 to 63 degrees, 

 or in the language of heat, the coal gives out 

 14,000 B. T. U. One B. T. U. can raise 778 Ibs. 

 one foot, or is equivalent to 778 foot-pounds. There- 

 fore, one pound of coal can raise 14,000 X 778, or 

 10,892,000 foot-pounds; this amount of power 

 would raise 7,000 Ibs. 1,556 feet. 



