THE STEAM-ENGINE. 



487 



steam is drawn off through the valve G on the ascent of the piston, and on the 

 descent is forced through a tube into a hot well H, for the purpose of feeding 

 the boiler through the feed-pipe I. In the top of the hot well H is a valve 

 which opens inward, and is kept closed by a ball floating on the surface of the 

 liquid. The pressure of the condensed air above the surface of the liquid in 

 H forces it through I into the boiler. When the air accumulates in too great 

 a degree in H, the surface of the liquid is pressed so low that the ball falls 

 and opens the valve, and allows it to escape. The air in H is that which is 

 pumped from the condenser with the liquid, and from which it was disen- 

 gaged. 



Let us suppose the piston at the top of the cylinder : it strikes the tail of 

 the valve T, and raises it, while the stem of the piston-valve R strikes the top 

 of the cylinder, and is pressed into its seat. A free communication is at the 

 same time open between the cylinder, below the piston and the condenser, 

 through the tube D. The pressure of the steam thus admitted above the pis- 

 ton acting against the vacuum below it, will cause its descent. On arriving 

 at the bottom of the cylinder, the tail of the piston-valve R will strike the bot- 

 tom, and it will be lifted from its seat, so that a communication will be opened 

 through it with the condenser. At the same moment, a projecting spring K, 

 attached to the piston-rod, strikes the stem of the steam-valve T, and presses 

 it into its seat. Thus, while the further admission of steam is cut off, the 

 steam above the piston flows into the condenser, and the piston being relieved 

 from all pressure, is drawn up by the momentum of the fly-wheel, which con- 

 tinues the motion it received from the descending force. On the arrival of the 

 piston again at the top of the cylinder, the valve T is opened and R closed, and 

 the piston descends as before, and so the process is continued. 



The mechanism by which motion is communicated from the piston to the 

 fly-wheel is peculiarly elegant. On the axis of the fly-wheel is a small wheel 

 with teeth, which work in the teeth of another larger wheel L. This wheel 

 is turned by a crank, which is worked by a cross-piece attached to the 

 end of the piston-rod. Another equal-toothed wheel M is turned by a 

 crank, which is worked by the other end of the cross-arm attached to the 

 piston-rod. 



One of the peculiarities of this engine is, that the liquid which is used 

 for the production of steam in the boiler circulates through the machine 

 without either diminution or admixture with any other fluid, so that the boiler 

 never wants more feeding than what can be supplied from the hot well H. 

 This circumstance forms an important feature in the machine, as it allows of 

 ardent spirits being used in the boiler instead of water, which, since they 

 boil at low heats, promised a saving of fuel. The inventor proposed that 

 the engine should be used as a still, as well as a mechanical power, in which 

 case the whole of the fuel would be saved. 



That part of Cartwright's piston which in the common piston is occupied 

 by the packing of gasket, already explained, was filled by a number of rings, 

 one placed within and above another, and divided into three or four seg- 

 ments. Two rings of brass were made of the full size of the cylinder, and 

 so ground as to fit the cylinder nearly steam-tight. These were cut into 

 several segments A A A, fig. 48, and were placed one above the other, so 

 as to fill the space between the top and bottom plates of the piston. The 

 divisions of the segments of the one ring were made to fit between the di- 

 visions of the other. Within these, another series of rings, B B B, were 

 placed, similarly constructed, so as to fit within the first series in the same 

 manner as the first series were made to fit within the cylinder. The joints 

 of the upper series of each set of rings are exhibited in the plan fig. 48 ; 



