52 ANNUAL OF SCIENTIFIC DISCO \ 7 ERY. 



therefore so much gain to the engine, excepting the power required 

 to work the air-pump, which must be deducted. The common 

 method of condensing, is to let the steam come in direct contact 

 inside of the condenser, with the cold condensing water, and keep 

 pumping out the hot, at 100, and supplying the condenser with cold 

 water. The principle of condensing the steam by the outside appli- 

 cation of water, is older than the injecting of cold water among the 

 exhaust steam, but it has always been considered an inferior mode of 

 condensation. In Miller's condenser an exhaust pipe conveys the 

 steam from the cylinder, after it has acted upon the piston, to the con- 

 denser. This exhaust steam, however, is allowed to pass into a 

 heating vessel, before entering the condenser, where it is condensed 

 in the inside of the tubes of the condenser, by the application of a 

 constant stream of cold water to the outside of the tubes. The con- 

 densed steam inside falls to the bottom of the condenser in the state 

 of water, from which it is pumped, and forced into the boiler, as pure 

 feed water, by two air pumps, which thus serve as feed pumps. 

 Before entering the boiler, it passes through a metallic vessel, and is 

 there raised by the exhaust steam to about the boiling point. The 

 great object in condensing the exhaust steam to save power, is to get 

 a good vacuum behind the piston, and the great object in saving fuel 

 is to return the water to the boiler as hot as it is possible to do so, 

 and in as pure a state as possible ; this is believed to be successfully 

 accomplished by this arrangement. There is an air chamber on the 

 top of the heater, to let the accumulated elastic gas and air in the 

 water escape from time to time ; this can easily be done by the engi- 

 neer, according to where the heater is situated, by the cock on the 

 top of the air chamber. It was a great improvement in sudden con- 

 densation, when the cold water was first applied inside of the cylinder 

 injected among the steam instead of on the outside, because it 

 requires so much cold water to condense the steam - - no less than 

 22.24 cubic inches of water to one of water converted into steam. 

 Watt endeavored, by his first condenser, to obtain enough of cooling 

 surface to condense the steam inside by using thin hollow chambers, 

 but he soon resorted to mixing the cold water with the steam again. 

 Hall's condenser, for the same purpose, consisted of a faggot of small 

 copper tubes, but this condenser, we believe, is nowhere in use. 

 Plenty of cooling surface can be obtained by pipes, &c., but owing 

 to the expansion and contraction of the metal, at the joints, there is 

 a continual tendency to leakage, and a leak destroys the whole object 

 of the condenser. To construct a condenser upon principles to 

 obviate the evils of leakage by the expansion and contraction of the 

 metals, has been the object and aim of Mr. Miller. The tubes of the 

 condenser are united by screw joints, with vulcanized india-rubber 

 between the flanges. The steam coming from the boiler, through the 

 heater, has free passage at once to all the condensing tubes. These 

 tubes are of a peculiar construction ; each one is double, and the 

 interior end, where the steam at first strikes it, is round and uncon- 

 nected, and free to expand and contract without affecting the joints. 



