RULES FOR CALCULATING THE STEAM ENGINE. 211 



Example. Let the height be 5 feet, and the number of horses' power 96. 



Square root of 5 = 2-28 

 2 



Divide by 5) 4-56 



0-91 

 Horse power 96 



546 

 819 



87'36 square feet for the grating. 



CHIMNEY. 



10. To find the area of a chimney for a steam engine. 

 RULE. For engines of 10 horse power and upwards the area of the chimney, in square 

 inches, should be 112 times the horse power divided by the square root of its height. (145.) 



Example. Required the area of a chimney for an engine of 40 horse power, the height 

 being 70 feet. 



Horse power 40 

 112 



Square root of 70 = 8'4) 4480,0 (533 inches 



420 



280 

 252 



280 

 252 



28 

 The area should therefore be 533 square inches. 



CYLINDER. 



11. To find the requisite thickness of a working cylinder. 



RULE. To the diameter of the cylinder in inches add 2'5 ; multiply the sum by the total 

 pressure of steam in Ifcs. per square inch in the boiler, and divide the product by 1900. The 

 result will express the thickness for strength, and half an inch may be added for wear. (247). 



Example. A cast iron cylinder 24 inches diameter is to be made for steam not exceeding 

 5 Ifes. per square inch on the safety valve ; required its thickness. 



