336 APPLIED SCIENCE 



boat of 1000 tons generally has an engine of 360 H. P. A 

 man-of-war usually has one horse-power for every ton. 



There are several kinds of horse-power referred to in the dis- 

 cussion of a steam engine; nominal, indicated, and actual or net. 



Nominal horse-power was a term used during the invention 

 of the steam engine to express the amount of work an engine 

 could perform during a given time. 



Indicated horse-power is obtained by multiplying the mean 

 effective pressure in the cylinder in pounds per square inch, 

 by the speed in feet per minute, and dividing the product by 

 33,000. 



Actual or net horse-power is the difference between the 

 indicated horse-power and the amount of horse-power ex- 

 pended in overcoming friction. 



EXAMPLE. What is the horse-power of an engine that can pump 

 68 cu. ft. of water from a depth of 108 ft.? 



1 cu. ft. of water = 62^ Ibs. 

 68 X 62^ = 4250 Ibs. 

 4250 X 108 = 459,000 ft.-lbs. 



459,000 153 



33,000 11 



= 13f? H.P. = 13.9 H.P. . 



377. Corrosion of Pipes. If the feed water contains lime 

 salts, a deposit will be formed in the economizer and feed 

 connection which will more or less effectually protect the 

 pipes from internal corrosion ("rusting" or "eating away"). 

 If, however, the water is very free from Jime, and air is intro- 

 duced by the feed pump, internal pitting (small hollows) will 

 be formed. Considerable damage may then be done before 

 the danger is discovered and steps taken to prevent further 

 mischief. 



