Chap. XXI. STEAM CONSIDERED AS A MOVING POWER.

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The boiler is generally made of iron, though formerly copper was used; and by meansof a pipe the steam passes from the boiler to the upper nozzle G, and by the perpendi-

Fig.1963.

ENGINE AT THE ALBION MILLS.

cular steam-pipe I, to the lower steam nozzle K : in the nozzle G there is a valve, whichwhen open admits steam into the cylinder above the piston IB, through the horizontalsquare pipe at the top of the cylinder, and in the lower steam nozzle K there is anothervalve like that at D, which, when opened by the pin of the plug-tree, admits steam intothe cylinder below the piston. In the upper exhaustion nozzle, H, there is a similar valve,which when open allows steam to pass from the cylinder above the piston into the educ-tion-pipe J, which conveys it to the condensing vessel M, where it meets with the jetof the injection from the cock N, and is reduced to water; and in the lower exhaustionnozzle L, there is also a valve, which when open allows the steam to pass out of thecylinder below the piston into the condenser M.

The engine being at rest, the cylinder quite cold, and the condenser cistern full of water,when the water in the boiler begins to boil, steam will enter by the small pipe f into thespace between the cylinder and the heating case E, which will expel the air contained inthat space, and between the two bottoms of the cylinder, at a cock fixed in the outer bottom,which, when all the air is expelled and the cylinder thoroughly warmed, is to be shut, andthe water which may be formed in these spaces during the working of the engine will issueby the inverted siphon e.

The first operation after this state is to open all the four valves, G, H, K, L; the in-jection cock being shut, the steam will drive the air out of the pipes I and J, and out ofthe condenser M, through the blow-pipe and its valve O, and as soon as this is succeededby a sharp crackling noise in the cistern O, the valves are to be shut, until it is thoughtthat the steam which has entered is entirely condensed; the same operation is to berepeated, giving a longer time to cool between the times of blowing, until it is found uponopening the injection cock some water will enter, and the barometer shows some degree ofexhaustion, after which the repetition of blowing will soon empty the cylinder of air. Thepiston being then at the top of the stroke, the valves G and L are to be opened, and thefly-wheel m turned by hand about \ of a revolution or more in the direction in which itis intended to move; the steam which is then in the cylinder will pass by L into thecondenser, when, meeting with the jet of water from the injection cock, it will be convertedinto water, and the cylinder thus becoming exhausted, the steam entering by the valve G willpress upon the piston, and cause it to descend, while by its action on the working beam,through the piston rod, it pulls down the cylinder end of the beam, and raises up theouter end, and the connecting rod A, which causes the planet-wheel i to tend to revolveround the sun-wheel j: but the former of these wheels being fixed upon the connectingrod, so that it cannot turn upon its own axis, and its teeth being engaged in those of the