160 History of Mechanical Inventions, and 



formance of which I intend making some observations, is 80 inches. The 

 piston making a stroke of 10 feet approaches to within 3 inches of the 

 cylinder cover. The air pum.p is 36 inches in diameter. The load of the 

 engine is (forcing) viz. 273 feet of 11 inches in diameter 



462 16 



55 16.5 



63 12 



It works without intermission, and in the month of January made 274,320 

 strokes, consuming 2034 bushels of Swansea coal. The packing of the 

 piston may be supposed to be about six inches in depth ; the area of the 

 rubbing part is therefore 10,472 feet ; but the friction on every foot of the 

 surface of a piston is said (Farey on the steam engine,) to be about 2S$lbs. 

 the amount of this is consequently - - 3015,936 lbs. 



The area of the rubbing part of the air pump is 3,927 feet, 



and estimating the friction at 144/ta per foot, - 565,488 



The depth of the packing surrounding each of the forcing 

 pistons may be estimated at 9 inches, and the circumfe- 

 rence of the whole of them 14,5299 feet ; the friction per 

 foot being considered the same as for the air pump, 1569, 2256 



The mean temperature of the column of water being esti- 

 mated at 69 c , its weight is about - - 59662,349 



The whole load of the engine being - - 64812,9986 lbs. 



Or 10,917 lbs. per square inch of the area of the piston, or equal to 22,216 

 inches of mercury. But the pressure of the steam in the boiler is about 

 equal to a column of 71,15 inches of mercury; therefore, the steam from 

 the boiler must occupy about .38224 of the length of the cylinder. Per- 

 haps .35 may be nearer the truth, a small portion more being required to 

 overcome the friction of the working parts ; this gives 24.9 inches of mer- 

 cury as the pressure of the steam contained in the cylinder at the termi- 

 nation of the working stroke. 

 The capacity of the cylinder is about, - 349,07 cubic feet ; 



this must at every stroke be completely filled. 

 The space between the piston and cylinder cover, nozle, 



&c. 10 cubic feet to be, 65 filled every stroke, is about 6.5 



Therefore 355,57 cubic feet of steam of the pressure of 24.9 inches of mer- 

 cury are to be expended at every stroke. 



355,57 X 274320 _ 47954 75 cubic feet which reauce( j to the pressure of 



2034 r 



30 inches of mercury 39802,4425 feet of steam ; or 23,03382 cubic feet of 

 water converted into vapour, of the atmospheric pressure, by the combus- 

 tion of a bushel (84 lbs.) of coal, exclusive of that condensed in the case. 

 The increased weight of the column of water in the pumps, arising from 

 its compression, seems too little to be worthy of a separate investigation. 

 The load on the air pump is at the commencement very little ; but towards 

 ^he termination of the stroke, its piston is subject to the pressure of the 



