In order to increase the force of the steam, Papin proposed to introduce a red hot heater, through G, but this was a clumsy contrivance, of no value ; and indeed the whole machine, though ingenious, could not be put in comparison with the previous invention of Savery.
Dr. Gravesende, having come to England as secre tary to the Dutch embassy in 1716, went through a course of experimental philosophy with Dr. Desagu :iers. When they were considering Savery's steam en gine, it appeared to them that there was a great waste of steam by its continually acting upon the re ceiver without intermission, since it became useless till it had heated the surface of the water in the re ceivers. They therefore made a model which could work either with one or two receivers, and they soon found by it that, "one receiver could be emptied three times, while two succeeding ones could be emptied only once a piece." Hence they concluded, that such an engine would save a third more water, and be erected at only half the expense.
This ingenious contrivance is shown in plate DV, Fig. 1, where A is the receiver of copper communi cating at bottom with the making and forcing pipes between E and G, and at top with the steam pipe at D, and the rejecting pipe at I. The boiler II, which is also of copper, contains at least five times more than the receiver, round which the fire and flame are con ducted at T, T, T. It has a copper cover screwed, in which contains the steam pipe CD communicating from the boiler to the receiver, and guage pipes N It, 0 o, with a valve at P, kept down by the steelyard PQ and weight Q. The surface SS of the water in the boiler must be lower than the bottom of the short guage pipe at o, and higher than the bottom of the long one at 71. The steam cock DI has its key K kept down by the screw L held by the arm DI., while the handle K is either turned to k to receive the steam is suing from the boiler, or to K to shut off the steam and admit a jet of cold water coming from the ascend ing pipe EE2 through the cock M, the mechanism of which is shown in detail in Fig. 2, where 1 is the screw which, passing through the stirrup 2, presses on the piece of cast iron :3, made tight to the brim under it by double canvas, while the returns of the stir rup draw up the ring 4 under the brim to support it; 5, 6, 7, shows the key of the stop cock with a hole on the side at 6, which passes down through the bottom of the key to throw down alternately into the receiver the steam and the jet or injection. There is a notch in the key at 7 to receive the water from the force pipe, and carry it to the boiler, when it receives a fresh supply of water. The annexed section of the steam
cock and key will make its construction perfectly in The horse or pipe EEGZ, with several elbows, is soldered at E to the forcing pipe EE2. The sucking pipe ZI-[ is soldered to it at Z, and the receiver at F. This horse contains the sucking valve at G, and the forcing valve at F, which are easily got at by unscrew ing I to loosen the strap 2, and let down the flanch 3, as shown in Fig. 2. The cistern R communicates with the forcing pipe by a cock and small branch V to fill the forcing pipe when required. A spreading plate I is used to make the steam and the water be alternately divided into little jets, and I, c represents the surface of the steam pushing down the water in order to drive it up again into the force pipe EE through the valve E. The door of the fire place is shown at V, and the ash hole at W.
This engine operates as follows. Take off the steel yard PQ, and open the cock 0 of the short guage pipe 0 o, then holding up the valve by a long nail, pour in water at the valve, which will blow out the air at 0 till the surface of the water rises above the bottom o of the gunge pipe, when the boiler will be sufficiently filled. Having then stopped the communication be tween the steam cock DI and the boiler, and shut the two guage cocks at N and 0, replace the steelyard on the valve with its weight 0 near P, and light the fire at T. As the fire is increased remove the weight Q, notch by notch, till it conies to the last notch at Q, and see that no additional weight is put to it.
When the steam begins to lift the safety valve P, and when the receiver A has been filled with water, which is done by taking out the key of the cock under the screw I., and opening the cocks Y and M, turn the handle of the steam-cock on the receiver from K to k to admit the steam from the boiler along CD, first opening it partially, and then fully. The steam will now spread through the small holes of the plate at I, and pressing on the surface of the water at b c, will force it through the valve F, and up the pipe EE. This pipe being now full, and the cock M open, turn back the handle from k to K, and a jet of cold water will spout through the spreading plate I among the steam, which it will immediately condense, and the air pressing on the water in the well at II will push it up into the receiver A, and will force it up I. The handle being turned to k as formerly, the steam will be again admitted, and will again draw the water up the pipe EE into the cistern R.