340 
EXPLANATION OF THE PLATES. 
PLATE XII. 
This plate shows an elevation of a single acting engine, as executed by Messrs. 
Boulton and Watt. The boiler a is inclosed in a case of brickwork, and the steam 
passes by the steam pipe b, to the cylinder c, which is firmly attached to the floor 
of the engine room, by the bolts d, d: its upper end is covered by the lid e, 
through which the piston rod k slides in an air-tight box called a stuffing box. 
The beam f g moves on its axis or gudgeon at h; and the bearings in which the 
gudgeons work are sustained by the floor and wall i. 
The pump rod j, carrying a counter-weight, is suspended at the end g of the 
beam; and both it and the piston rod k are connected by a parallel motion appa 
ratus to the working beam f g. See art. 492. 
The condensing cistern is at m, and contains the air pump n, the condenser, and 
hot well o: a continued supply of cold water is procured by the action of the cold 
water pump p, and the excess is carried off by a waste pipe to the well q ; the 
whole of the external part of the apparatus being kept by that means at the lowest 
temperature possible. 
The upper steam valve is at r, and the lower at s, and the exhaustion valve at t. 
See Fig. 5. Plate v. These valves are moved by the plug tree v, which is furnished 
with tappets to give motion to the levers acting on the valves r, s, t. See art. 478. 
The pump to raise water from the hot well o, to supply the boiler, is at u, and 
the water is conveyed by the pipe w w to the small cistern x on the top of the feed 
pipe, which is provided with a valve, and acted on by a lever connected by a wire 
passing down through a stuffing box y, to a stone float in the boiler, which by its 
descent opens the valve, and allows the admission of an additional supply of water 
when it is required, (art. 251.) 
In order to prevent concussion, two blocks 1, 2, are fixed across the upper side 
of the beam, and extend on each side so as to strike on four wooden springs, on 
the floor which supports the beam. See art. 549. 
For large engines the beam is in two parts, with a space between them, as 
shown in Fig. 3. Plate x. 
The proportions of the single engines are given in Sect. vi. art. 406—413 ; the 
application, in art. 572, 573. 582. and 587 ; their effects, art. 576 ; and their power, 
and consumption of fuel, Table n. art. 663.