THE STEAM-ENGINE. 



425 



Fig. 7. 



ing toward I, fitted with a piston K, which served the office of the air-pump, 

 being worked by the hand. This piston, K, had valves in its opening upward. 

 These condensing pipes and air-pump were immersed in a small cistern, filled 

 with cold water. The steam was conveyed by the steam-pipe S to the bottom 

 of the cylinder, a communication between the top and bottom of the cylinder 

 being occasionally opened by a cock, C, placed in the branch pipe. The 

 eduction pipe leading to the condenser also had a cock, L, by which the com- 

 munication between the top of the cylinder and the condenser might be opened 

 and closed at pleasure. In the commencement of the operation, the cock N 

 admitting steam from the boiler, and the cock L opening a communication be- 

 tween the cylinder and the condenser, and the cock C opening a communica- 

 tion between the top and bottom of the cylinder, being all open, steam rushed 

 from the boiler, passing through all the pipes, and filling the cylinder. A 

 current of mixed air and steam was thus produced through the eduction pipe 

 E, through the condensing pipes F and G, and through the air-pump I, which 

 issued from the valve H in the eduction pipe, and from the valve in the air- 

 pump piston, all of which opened upward. The steam also in the cylinder 

 passed through the hole drilled in the piston-rod, and escaped, mixed with air, 

 through the valve in the lower end of that rod. This process was continued 

 until all the air in the cylinder, pipes, and condenser, was blown out, and all 

 these spaces filled with pure steam. The cocks L, C, and N, were then closed, 

 and the atmospheric pressure closed the valve H and the valves in the air-pump 

 piston. The cold surfaces condensing the steam in the pipes F and G, and in 

 the lower part of the air-pump, a vacuum was produced in these spaces. The 

 cock C being now closed, and the cocks L and N being open, the steam in 

 the upper part of the cylinder rushed through the pipe E into the condenser, 



