To obtain a greater power by a complicated force of steam, an engine was constructed by Mr. JONATHAN HORNBLOWER (of Penrhyn, Cornwall), in which theprinciples of-condensation and e‘pansion were made subservient to a new application ; for this invention he obtained a patent in 1781, the specification of which is here transcribed.
"First,—I use two steam vessels, in which the steam is to act, and which in other steam-engines are called cylinders. Secondly,—I employ the steam, after it has acted in the first vessel, to operate a second time in the other, by permitting it to expand itself, which I do by connecting the vessels together, and forming proper channels and apertures whereby the steam shall occasionally go in and out of the said vessels. Thirdly,—I condense the steam by causing it to pass in contact with metallic substances, while water is applied to the opposite side. Fourthly,—to discharge the engine of the water .employed to condense the steam, I suspend a column of water in a tube or vessel constructed for that purpose, on the principles of the barometer, the upper end having open com munication with the steam vessels, and the lower end being immersed in a vessel of water. Fifthly,—to discharge the air which enters the steam vessels with the 'condensing water, or otherwise, I introduce it into a separate vessel, whence it is protruded by the admission of steam. Sixtbly,—that the condensed vapour shall not remain in the steam vessel in which the steam is condensed, I collect it into another vessel, which has open communication with the steam vessels, and the water in the mine, reservoir, or river. Lestly,—in cases where the atmosphere is to be employed to act on the piston, I use a piston so con structed as to admit steam round its periphery, and in contact with the sides of the steam vessel, thereby to prevent the external air from passing in between the piston and the sides of the steam vessel." A more intelligible description of this engine was subsequently given by Mr. Hornblower in the Encyclopedia Britannica, which thus explains it. [See cut in the preceding page.] Let A and B represent two cylinders, of which A is the largest; a piston moves in each, having their rods C and D moving through collars at E and F. These cylinders may be supplied with steam from the boiler by means of the square pipe G, which has a flange to connect it with the rest of the steam-pipe. This square part is represented as branching off to both cylinders; c and d are two coas which have handles and tumblers as usual, worked by the plug-beam W. On the fore side of the cylinders is represented another communicating pipe, whose section is also square, or rectangular, having also two cocks, a b. The
pipe Y immediately under die cock b establishes a communication between the upper and lower parts of the cylinder B, by opening the cock b. There is a similar pipe on the other side of the cylinder A, immediately under the cock d.
When the cocks a and a are open, and the cocks b and d are shut, the steam from the boiler has free admission into the upper part of the small cylinder B, and the steam from the lower part of B has free admission into the upper part of the great cylinder A ; but the upper part of each cylinder has no communi cation with its lower part. From die bottom of the great cylinder proceeds the eduction pipe K., having a valve at its opening into the cylinder; it then bends downwards, and is connected with the condenser. Lastly, the pump-rods cause the outer end of the beam to preponderate, so that the quiescent position of the beam is that represented in the figure, the pistons being at the top of the cylinder. Suppose all the cocks open, and steam coming in copiously from the boiler, and no condensation going on in L, the steam must drive out all the air, and at last follow it through the valve Q. Now shut the cocks b and d, and open the escape-valve of the condenser ; the condensation will immediately commence and draw off the steam from the lower part of the great cylinder. There is now no pressure on the under side of the piston of the great cylinder A, and it immediately descends. The communication Y between the lower part of the cylinder B, and the upper part of the great cylinder A being open, the steam will go from the lower part of B into the space left by the descent of the piston A. It must therefore expand, and its elasticity must diminish, and will no longer balance the pressure of the steam coming from the boiler, and pressing above the piston of B. This piston, therefore, if not withheld by the beam, would descend till it came in equilibria, from having steam of equal density above and below it. But it cannot descend so fest, for the cylinder A is larger than B, and the arch of the beam, at which the great piston is suspended, is no longer than the arm which supports the piston of B; therefore,when the piston of B has descended as far as the beam will permit it, the steam between the two pistons occupies a larger space than it did when both pistons were at the top of their cylio,. dere, and its -density diminishes as its bulk increases. The steam beneath the small piston is, therefore, not a balance for the steam on the upper side of the same, and the piston B will act to depress the beam with all the difference of these pressure.