in the suction pipe, (e), forces open the valve d 1, and, passing through fi, enters the vessel A 1, and ascends in it until it attains such a height that its own pressure, together with the elastic force of any uncondensed vapour, balance the atmospheric pressure. This is the first part of the process, exactly similar, it will be seen, to the experiment described in paragraph 40. 197. The vessel A, being thus filled, or nearly filled, with water, the connection between it and the boiler is again opened. The steam, issuing from the boiler, presses upon the surface of the water in A 1, and expels the water, which, having no other course, is forced through the valve c, into the force-pipe b, where it ascends, and is removed as required. This is the second and last part of the action of this engine, exemplifying, on the large scale, the experiment described in paragraph 107. 198. These two vessels were used alternately for the preceding operations-the force of steam emptying one (A 1) of water, by pressing the water up the forcepipe; while, in the other (A 2), the vacuum was being formed, and the atmospheric pressure was filling it with water. Then, the first (A 1) being full of the steam which had forced out the water, the jet of water was turned upon it, while steam was admitted to press upon the water in the other (A 2), the engine being thus kept in continual action, or, at least, with very little intermission. 199. There is little of interest in the boiler used for this engine. The boilers of Newcomen and Watt's engines, will be fully described afterwards. The gauge pipes for ascertaining the quantity of water in the boiler, were the invention of Savery, and he applied to his boiler the safety-valve, which was contrived by Papin for his Digester. 200. Savery's engine is a very beautiful piece of mechanism; but, as it never came extensively into use, and, though afterwards improved by Desaguliers and others, was abandoned upon the appearance of Newcomen's, we shall do little more here than point out briefly the defects under which it laboured, as well as the merits of its ingenious inventor. 201. By condensing the steam, and thus giving effect to the atmospheric pressure, he raised water cheaply and easily to a height of about twenty-six feet above its level, a clear gain of power; and, by the force of steam, he was able to elevate this water sixtyfour feet higher; thus raising it, in all, by the combination of the two modes, ninety feet above its level, certainly a great step in advance of any previous method. 202. Savery suggested the application of his engine, also, to raising water for working mills, raising water to houses for domestic purposes, and extinguishing fires, supplying cities with water, draining fens and marshes, propelling ships; but he does not appear to have drawn out or published a plan for any other application, except that of raising water. Savery died about 1717. He was much esteemed and well spoken of by his contemporaries. He had the satisfaction of seeing his invention applied to practice. His engine was actually applied to draining mines and raising water for gardens, as we learn from statements by himself and others. 203. But it laboured under considerable disadvantages. One of the principal of these was, that it must be erected not more than about twenty-seven or twenty-six feet above the level of the water to be raised. Were the vacuum perfect in the copper vessel, the atmospheric pressure would fill it with water, if its upper part were 33.87 feet above the water to be raised. But the vacuum is never perfect; some vapour always remains, opposing the atmospheric pressure; so much that it was found that the water could not be raised much above twenty-six feet. Here, then, was a great drawback on the engine; so near the bottom of a mine, it would be very apt to be destroyed by the water rising, especially if, from any cause, its action should be suspended for a day or two. 204. Next, engines would be required at every 90 feet, as the vessels could not bear the enormous pressure of steam (nor the boilers the heat) which would force water up to a height greater than 64 feet. 64 feet added to the 26 feet which the water was raised by atmospheric pressure, make 90. To balance the atmospheric pressure, the steam which acts on the water in the copper vessel must have an elastic force of 14.7 pounds on the square inch. Of course, it exerts no force in pressing the water up the force-pipe till it exceeds the atmospheric pressure. As the atmospheric pressure is equal to a column of water, 33.87 high, the steam must acquire the elastic force of another atmosphere-14.7 pounds per square inch more-to force the water to a height of 33.87 feet in the forcepipe; and 14.7 pounds more, to raise it 67.74 feet; in all, 44.1 pounds on the square inch, an enormous pressure on the boiler and copper vessels. 14.7 pounds of this are balanced by the external atmospheric pressure, leaving a bursting pressure of 29.4 pounds on every square inch. The vessels cannot with safety bear more than this-so that the action of the engine is limited to raising water 90 feet above its level; hence in mines, an engine would be required for every 15 fathoms (90 feet,) and the whole would be suspended when one got out of order. Indeed, Mr Savery himself recommended that the engines should not be applied for a lift of more than from 60 to 80 feet. 205. In the third place, the engines required to be small-large ones could not be made sufficiently strong so that they raised but a small quantity of water, and, at each 15 fathoms, several would be required. 206. Lastly, the expense of fuel for these engines was very great, from two causes :-First, The high pressure of the steam, which (by the table in par. 126,) would require to be of the temperature 274° Fahrenheit, in order to produce an effective pressure of 44.1 pound on the square inch; and, second, from the waste of heat in the alternate cooling and heating of the copper vessels, and in the condensation of the steam before it heated the surface of the water in the copper vessel up to its own temperature. There was also considerable risk of explosion. 207. The part of Savery's engine, however, in which water is raised by atmospheric pressure, has been advantageously applied to raise water short distances, as twenty to twenty-five feet. In this case, the engine was made self-acting, and there was an airvalve by which the air which entered with the steam and water was blown out-this was necessary that the vacuum might be as complete as possible. Several engines were constructed upon this plan by Mr Rigby in Lancashire, and one in London. The water raised turned an overshot water-wheel by which the machinery was impelled in the usual way. In some situations, Savery's engine might still be used with advantage. SECTION III: PAPIN AND DESAGULIERS. PAPIN.-1707. 208. In 1707, Papin published, at Cassel, a tract entitled "New method for Raising Water by the Force of Fire." His plan was essentially the same as that of one part of Savery's-that in which the water was raised by the elastic force of the steam. The chief differences were, that the vessel in which the steam acted on the water was cylindrical, and that the steam did not come into direct contact with the water, but was separated from it by a movable float or piston. This was a decided improvement, less steam being thereby lost by condensation. The steam, after acting on the water, was permitted to escape into the air. This engine does not possess much merit: not using the steam for making a vacuum thereby to take advantage of the atmospheric pressure, it was decidedly inferior to Savery's, and never came into use. 209. Papin proposed this engine as a means of giving motion to a water-wheel, the water raised being made to fall upon the floats of the wheel, and turn it round in the usual manner. That the stream might be continuous, an air-vessel was interposed between the opening from which the water issued to the wheel and the receiver from which it was expelled by the steam. The air became compressed in the air-vessel, and by its elastic force in expanding again, pressed out the water in a continuous stream. The work in which this engine was described, was not published till nine years after the date of Savery's patent, and in it Papin |