HNE. 



tion, if not removed, would soon obstruct and altogether arrest 

 the action of the machine. 



This air, as well as the warm water deposited in the bottom of 

 the condenser, is withdrawn by a pump, A, called the AIII-PFMP, 

 because of its use in the removal of the air just mentioned. In 

 the piston of this pump are valves which open upwards, so that 

 when the piston descends the water and air force themselves 

 through the valves, and when it ascends it lifts the water and air 

 which have thus passed through the valves, and throws them into 

 a small reservoir, D, through a valve, K. This reservoir, D, is 

 called the hot cistern, the water deposited in it having a tempera- 

 ture more or less elevated, owing to the steam which has been 

 condensed by it. 



The ascent of the piston of the air-pump has also the effect of 

 drawing by suction, as it is commonly called, the water and air 

 from the condenser, B, through the valve M into the bottom of the 

 barrel of the air-pump, from which they cannot get back into the 

 condenser, inasmuch as the valve, M, opens towards the air-pump, 

 and their returning pressure only closes it more firmly. 



39. The continual affluence of the steam to the vessel B, and the 

 water constantly passing through it, the air-pump, and the 

 cistern, D, would at length raise the temperature of the water in 

 the cistern, c c, in which the condensing apparatus is immersed, 

 to such a point that the jet projected into the condenser would be 

 no longer cold enough to condense the steam. 



To prevent this a pump, called the cold-water pump, is pro- 

 vided, which throws into the cistern a sufficient quantity of cold 

 water. This water is introduced near the bottom of the cistern, a 

 waste-pipe being provided at the top by which the warm water, 

 which always collects near the upper surface, flows off. In this 

 way the temperature of the water in the cistern, c c, is kept 

 sufficiently low, notwithstanding the heat proceeding from the 

 condensing vessels. 



40. To prevent the accumulation of warm water in the cistern, 

 D, a pump called the hot- water pump is connected with it, by 

 which the water is drawn off from it and transferred to the feeding 

 apparatus of the boiler. Thus a part of the heat given out by the 

 condensed steam, and which has already done duty in working 

 the piston, is returned to the boiler to take another round of duty. 



Thus it appears that the condensing apparatus consists of the 

 cold cistern, c c, the cold-water pump which supplies it, the con- 

 denser, B, the air-pump, A, the hot cistern, D, and the hot-water 

 pump, which draws the water from it. 



32 



