526 Siphons used by Chemists. [Book V. in operation by the lungs. Moreover cocks and valves of metal are acted on by acids, and in some cases would affect or destroy the properties of the fluids themselves. No. 258 No. 259. No. 260. No. 261. No. 262. No. 263. No. 258 shows how hot or corrosive liquids may be drawn off from a wide mouthed bottle or jar. The short leg of a siphon is inserted through the cork; and also a small tube, through which the operator blows, and by the pressure of his breath forces the liquid through the siphon. No. 259 represents a siphon sometimes employed by chemists. When used, the short leg is first placed in the fluid to be decanted, the flame of a lamp or candle is then applied to the underside of the bulb; the heat rarefies the air, and consequently drives out the greater part of it through the discharging orifice. The finger is applied to this orifice, and as the bulb becomes cool the atmosphere drives up the liquid into the void and puts the instrument in operation. No. 260 is a siphon by M. Collardeau. It is charged by pouring a quantity of the fluid to be decanted into the funnel; the bent pipe attached to which terminates near the top of the discharging leg. The fluid in descending through this leg bears down the air within it, on the principle of the trombe, and the atmosphere drives up the liquid in the reservoir through the short leg. In experiments with this instrument we invariably found the contents of the charging tube drawn into the siphon whenever the orifice of the discharging leg was not made smaller than the bore of the receiving one. By not attending to this, such siphons will only act as long as water is poured into the funnel. No. 261. A glass siphon for decanting acids, &c. It is charged by sucking, and to guard against the contents entering the mouth, a bulb is blown on the sucking tube. The accumulation of a liquid in this bulb being visible, the operator can always withdraw his lips in time to prevent his tasting it. No. 262 is designed to retain its contents when not in use, so that on plunging the short leg deep into a liquid the instrument will operate. This effect however will not follow if the end of the discharging leg descend below the flexure near it, and if its orifice be not contracted nearly to that of a capillary tube. No. 263 is a siphon by which liquids may be drawn at intervals, viz. by raising and lowering the end of the discharging leg according to the surface of the liquid in the cistern. Our own labors have developed some novel modifications of the siphon. No. 264 is charged by an apparatus designed as a substitute for the syringe. (See No. 255.) The sucking tube of an ordinary siphon is made to pass through the centre of a much larger pipe. This is closed at the bottom, open at top, and its length equal to that of the short leg. A moveable tube open at bottom and closed above is fitted to slide in the last, and is of such a bore that the space between its sides and the exhausting tube Chap. 6.] Ewbank's Siphons. 527 equals the capacity of the siphon. To use this instrument, fill the wide tube with water or some other fluid, and place the short leg into the liquid to be decanted; then close the orifice of the long leg with the finger, and raise the moveable tube (by the ring attached to it) and the siphon will be charged. In using this instrument, the fluid by which it is charged does not mix with that which is decanted, as in No. 260. The apparatus is more simple than a syringe and is not liable to be deranged. By using mercury both the length and bore of the charging tubes may be greatly reduced. As these tubes themselves constitute a siphon, (see No. 238,) the upper end of the small exhausting one should extend a little above that which contains the charging fluid, lest this should occasionally rise over the orifice-in which case the whole would be drawn off. A description of this siphon was published in the Journal of the Franklin Institute for November, 1834. 100011 No. 264. No. 265, No. 266. Nos. 265-6 represent another mode of charging siphons on the same principle, but the apparatus is more simple and is accompanied with some peculiar advantages. The siphon itself has no exhausting pipe attached to it, but is a bent tube simply. It is put in operation by means of a moveable tube of about the same length as the discharging leg, and having the bottom closed and a lip or spout formed on its upper edge. This tubular vessel is filled with water (or other fluid) and the long leg of the siphon inserted into it. The short leg is then placed into the liquid to be decanted and the moveable tube drawn gently down. The air within becomes rarefied and the instrument charged in consequence of the vacuity left in the long leg by the receding liquid. The moveable tube may then be wholly withdrawn or not as circumstances may dictate. If the liquid is to be decanted at intervals, or the stream increased or diminished, the tube should be used; thus, to lessen or stop the discharge, slide up the tube and as the lip approaches to a level with the surface in the reservoir the stream will become less and less, and by raising it still higher, as in No. 265, entirely stopped. Hence the instrument acts as a perfect cock, by which the liquid may be discharged in single drops or in a full stream, and unlike the ordinary brass taps, it can never leak nor require repairs. The apparatus also performs the part of a guage, viz. by accurately indicating the surface of the fluid within any vessel to which it is attached. Suppose we wish to know the quantity of liquid remaining in a 'demijohn, or other close vessel, after drawing off part by one of these siphons; all that is required is to slide up the tube till the liquid barely drops from the lip-its surface in the tube will then be on the same level as in the demijohn. If the moveable tube be made of glass, the quantity left can always be known at sight, because its surface in the tube would always be visible. A device of this kind might be employed to draw off and to guage the 528 Ewbank's Siphons. [Book V. contents of standing casks. It would be better to make the discharging leg of this siphon of rather larger bore than the short one, since the rarefaction would then be more perfect. The discharging leg must always be inserted in the moveable tube before the short one is placed in the liquid to be transferred. (See Journal of the Franklin Institute for July and November, 1834.) No. 267 is formed of a conical tube, and charged by the act of placing it in the fluid to be transferred. The end of the long leg is first closed tight by the finger, and the short one then immersed as deep as can be conveniently in the liquid. The air being thus confined prevents the liquid from entering, but when the finger is withdrawn, it is urged up the short leg by the hydrostatic pressure of the column over the orifice of the latter, and the momentum of the large volume contained in the lower part drives sufficient over the bend to put the instrument in operation. The action of this siphon depends upon the same principle as the spouting tubes described in the last chapter. This siphon is in fact merely one of these bent into a proper form. The bend should be a regular curve in order to present as little obstruction as possible to the liquid in passing over it should also be short, so as to require less of the passing fluid to fill it than a longer one. The proportions of the different parts of these siphons should approach those represented in the cut. Small siphons on this plan are limited in their application to those cases where the short legs can be immersed half their depth or more; but the application of large instruments increases with the depth. (See No. 226 and remarks upon it, page 499.) Nos. 268-9 are blowing siphons, being charged by blowing with the mouth through the tubes connected to the orifices of the discharging legs. This mode of producing a vacuum in one pipe by blowing air through another is sufficiently explained in a previous chapter. In No. 269, the junction of the siphon with the blowing tube is flush or smooth in the interior of the latter, and whenever this is the case a conical ajutage must be added as represented, or the instrument cannot be charged. (See remarks on blowing tubes, pp. 486-7.) The better way is to make the siphon like No. 268, in which a part of the leg projects into the blowing tube and diverts the current of air from the lungs over the orifice, as in Nos. 205-'6, '7, and '13. These are more readily charged than the others, and although they will operate without the conical ajutage, they are much easier charged with it. By such siphons water may be raised one or two feet by a smart puff. They are safe and convenient to transfer acids, &c. as there is not the least danger of receiving any portion into the mouth, as when sucking siphons are used. Siphons are now used, as they were by the Egyptians in Heron's time, to convey water to considerable distances. When they are laid over ground that is elevated from 20 to 25 feet above the spring, a quantity of air is disengaged from the water at the highest parts of the tube, and accumulating there is very apt to cause the action to cease. To prevent this, a close vessel, furnished with a cock and funnel at the top, should be connected at its bottom to the highest part of the siphon by a stop cock or valve. The air evolved from the water will collect in this vessel and should be occasionally drawn off in the following manner. Shut the lower cock and open the one attached to the funnel; then expel the air by filling the vessel with water and turn the cocks as at first. As fresh portions of air arise from the liquid, they will enter the vessel and drive the water down the discharging leg. When the ground is very uneven at the highest parts, the several eminences of the siphon should be connected by small tubes to the air-chamber. Chap. 6.] Water conveyed over rising grounds by Siphons. 529 We have known siphons from a quarter to half a mile in length, and formed of leaden pipes only half an inch in the bore continue running from nine to fifteen months without once stopping, although no air-vessels were attached to them. In one case the pipe was 1200 feet in length, the orifice of the discharging leg was but five or six feet below that of the receiving one, and the highest part of the tube was from 12 to 15 feet above the surface of the spring. An opinion is current with some writers, that the extreme elevation to which water can be carried by siphons was unknown to the ancients, and that Heron, the most celebrated writer of antiquity upon these instruments, was not himself aware of its limitation to about 30 feet. It is not clear that Heron was thus ignorant; but if he were, it would only show that in this department of the arts he was no practical man. That ancient plumbers and pump-makers, who prepared and laid large siphons were aware of the limitation there can be no doubt, just as the same class of mechanics were in modern times with regard to pumps, before philosophers were informed of the fact or able to account for it. As however siphons for conveying water over hills and to great distances have always been of rare occurrence, (comparatively speaking,) it is not at all surprising that even some hydraulic engineers should have been thus ignorant with regard to them, although familiar with the extent to which water can be raised by atmospheric pumps. If some of these men have talked of conveying water by siphons over mountains, we never hear them speak of raising it to equal elevations through the suction pipes of pumps. Daily experience in applying the latter to various depths prevented them from falling into the error. Baptist Porta, in the 19th Book of his Natural Magic, speaks of raising water by a siphon to the top of a high tower, and several old writers have the same conceit. This was in accordance with the ancient doctrine of the plenists, who denied the possibility of a vacuum. They attributed the ascent of liquids through siphons to nature's abhorrence of a void, and imagined the elevation to be unlimited. But these men were philosophers, whose practical knowledge was confined to portable experiments; had they been working pump-makers they would have known better; they would have become advocates for the opposite doctrine-vacuists. So long was the error of the plenists maintained, observes Switzer, "that I have seen a book of Machines, written even in Queen Elizabeth's time, by one Ward, an engineer, who ventur'd to give a sketch of a high hill, and a house at the bottom or side, over which, by a vast extended syphon, the water was to be convey'd from one vale to another." The author of the old treatise, entitled, Art and Nature,' quoted at pp. 321, 375, was of the same opinion. How to convey water over a mountain: this experiment is as easie to be performed as any of the former, and indeed after the same manner, for you must lay a pipe of lead over the mountain, with one end in the spring or water that you desire to convey, and the other end must lie somewhat lower; then open the pipe at the top of the mountain; stop both ends of the pipe, and with a tunnell fill the pipe full of water; then close it up exactly that neither ayer nor water may come out thereat; then unstop both the ends of the pipe, and the water will run continually," (p. 10.) Decaus appears to have been better informed, if we may judge from his remarks respecting the perpendicular length of pipes of atmospheric pumps. In large engines, he recommends that they be not made over 20 feet; and including the working cylinders, he says, "I am of opinion that it [the water] must not be constrained to rise more than thirty feet in height." The second plate of his "Forcible Movements" repre 530 Discharging Water above its Source by Siphons. [Book V. sents two atmospheric pumps placed one above the other, and the lowest one raised it from "24 to 30 feet," and the upper one "may raise it from thence 24 or 30 feet" higher. The "Forcible Movements," it will be remembered, was published about thirty years before the discovery of atmospheric pressure. Contrivances for discharging water from the highest part of siphons have often been proposed. They are to be met with in several old authors, and the principle of most of them may be found in the Spiritalia. They are however seldom employed, because circumstances on which they depend rarely occur; and other devices are preferable even under those circumstances. A descriptive account of a few of them may interest some machinists, and be serviceable to others, viz: by preventing them from expending their energies in devising similar things. Indeed in this respect books which contain accounts only of the best machines are not always the most useful to inventors. In whatever department of the arts these men exercise their talents they are almost certain to fall at one time or another on old devices, which appear to them both new and equal to similar plans in common use. Books therefore which describe rejected and antiquated contrivances are not so worthless as some persons imagine. One plan to raise water by a siphon consists in enlarging or swelling it out at or near the bend, or what amounts to the same thing, connecting the legs to an air-tight vessel; and when this becomes filled the communication between it and the legs is cut off by valves or cocks, and the contents drawn off. When this is done the vessel remains filled with air, which if admitted into the legs would stop the action of the siphon. It must therefore, in order to expel the air, be filled with some liquid to replace that drawn out. Suppose a siphon of this kind be designed to raise water for the supply of a dwelling, in or near which the vessel is placed, it may then be refilled with refuse or impure water, which on adjusting the cocks will pass down the discharging leg. Then after a short time elapses, the vessel will again be filled with fresh water, which may be again exchanged for the same quantity of impure. In locations where river, salt, or any other water can thus be exchanged for fresh, and it is desirable to do so, such devices are applicable. (In breweries, distilleries, &c. the descent of one liquid may thus be made to raise another.) It should however be observed that an equal quantity must be given for that received, and it must descend rather more than the latter rises. But when circumstances allow these conditions to be fulfilled, the apparatus is not always to be depended upon; air insinuates itself through the minutest imperfections in the pipes and cocks, and often deranges the whole. One of these siphons is described in Nicholson's Journal, 4to. vol. iv, and in vol. ii, of Gregory's Mechanics. Another in the Bibliotheque Phisico-Economique, which is copied in vol. x, of the Repertory of Arts, 2d series. Another is figured in Art and Nature, A. D. 1633, with two close reservoirs at the top; and Porta, in cap. 3, book xix, of his Magic, describes another, with the close vessel on the top of a tower: the discharging leg is described as terminating in another close vessel of the same size as the one above, and furnished with a cock and funnel through which to fill it, and another cock to discharge the contents: this charging vessel from his description appears to have been placed on the ground a little below the spring and then emptied-if so, the apparatus could not act. He does not appear to have been aware of the necessity of the contents of the lower vessel being discharged from the orifice of a pipe as much below as the receiving vessel on the tower was above the spring. The device (which he probably imperfectly copied from some older author) |