SECT, vi.] CONDENSING ENGINES. 189 



densing at a lower temperature than 1 60 : and to estimate correctly, the proper 

 force of the uncondensed steam should be inserted in the causes of loss of force for 

 each particular case. 



398. The engine may be regulated by cutting off the steam before the piston 

 has arrived at the top, and cutting off the injection sooner : further means of 

 regulation are described in Sect. vm. By cutting off the steam it acts expan- 

 sively, and a less quantity produces the effect. Water for the top of the piston, 

 and for the supply of the boiler, should be raised from the hot well. The quantity 

 of water required to supply the boiler being ascertained in cubic feet per minute, 

 (art. 395.) the fuel will be known by referring to art. 190. and the size of the 

 boiler by art. 225 or 229. 



In the case of the Chase Water engine, 



6" x -7854 x 81 /j-oQ + l^N 

 1480 ' \ 6 / 



2'4 feet of water per minute, or 144 cubic feet per hour ; and 8-22 Ibs. of caking 

 coal convert 1 cubic foot of water into steam ; therefore the quantity per hour will 



1183'7 

 be 1183-7 Ibs., or - 75 = 16 Ibs. per hour for each horse power. The boiler 



may be either rectangular or cylindrical, with the steam limited to 1 Ib. on the 

 circular inch. 



399. The atmospheric engine is applicable to raising water in most cases 

 where coals are abundant : the engine is simple in construction and in operation, 

 and does not require that accuracy of workmanship which is necessary for an 

 engine acting by steam pressure. On a small scale it has less advantage ; for 

 when the cylinder is not more than about 2 feet in diameter, the consumption of 

 fuel becomes great in proportion to the effect : the drainage of coal mines, and 

 raising water to supply towns, and for irrigation where fuel is cheap, are its proper 

 objects. 



400. Atmospheric engines with a separate condenser. The manner in which an 

 engine of this kind may be constructed, is shown in Plate vi. Fig. 2., where C is 

 the cylinder with its piston P : the steam comes from the boiler by the pipe S, and 

 by a slide B is let into the cylinder at D, or kept out. A is a pump with a solid 

 piston, to receive the condensed steam, air, and water, and expel it : the injection is 

 made into the pipe E ; and I is the injection cock : F is a cock to let out any air 

 that may collect below the piston p when the engine is at rest. To begin the 

 operation, the slide B must be raised above S, and steam admitted till all the air 

 be blown out at the valve Q ; the pistons being at the top in both the cylinder and 

 pump : then shut off the steam by the slide B, and open the injection ; and, in 

 consequence of the condensation produced by the jet, both the pistons will descend, 



