Expansive Principle applied. -- Failure of Roebuck, and Partnership with Bolton. -- Patent extended to 1800. -- Counter. -- Difficulties in getting the Engines into use.
(49.) The first machine in which Watt realised the conceptions which we mentioned in the last chapter, is that which was afterwards called his _Single-acting Steam Engine_. We shall now describe the working apparatus in this machine.
The cylinder is represented at C (fig. 12.)--in which the piston P moves steam-tight. It is closed at the top, and the piston-rod being very accurately turned, runs in a steam-tight collar B furnished with a stuffing-box, and constantly supplied with melted tallow or wax. Through a funnel in the top of the cylinder, melted grease flows upon the piston so as to maintain it steam-tight. Two boxes A A, containing the valves for admitting and withdrawing the steam, connected by a tube of communication T, are attached to the cylinder; the action of these valves will be presently described. Below the cylinder, placed in a cistern of cold water, is a close cylindrical vessel D, called the condenser, communicating with the cylinder by a tube T´, leading to the lower valve-box A. In the side of this condenser is inserted a tube, the inner end of which is pierced with holes like the rose of a watering-pot; and a cock E in the cold cistern is placed on the outside, through which, when open, the water passing, rises in a jet on the inside.
The tube S, which conducts steam from the boiler, enters the top of the upper valve-box at F. Immediately under it is placed a valve G, which is opened and closed by a lever or rod G´. This valve, when open, admits steam to the top of the piston, and also to the tube T, which communicates between the two valve-boxes, and when closed suspends the admission of steam. There are two valves in the lower box, one H in the top worked by the lever H´, and one I in the bottom worked by the lever I´. The valve H, when open, admits steam to pass from the cylinder _above_ the piston, by the tube T, to the cylinder _below_ the piston, the valve I being supposed in this case to be closed. This valve I, when open, (the valve H being closed,) admits steam to pass from below the cylinder through T´ to the condenser. This steam, entering the condenser, meets the jet, admitted to play by the valve E, and is condensed.