SIPHON

, or Syphon, in Hydraulics, a crooked pipe or tube used in the raising of fluids, emptying of vessels, and in various hydrostatical experiments. It is otherwise called a crane.

Wolfius describes two vessels under the name of Siphons; the one cylindrical in the middle and conical at the two extremes; the other globular in the middle, with two narrow tubes fitted to it axis-wise; both serving to take up a quantity of liquid, and to retain it when up.

But the most usual Syphon is that which is here represented; where ABC is any crooked tube, having two legs of unequal lengths; but such however that, in any position, the perpendicular altitude BD, of B above A, when AB is filled with any fluid, the weight of that fluid may not be more than about 15lb. upon every square inch of the base, or equal to the pressure of the atmosphere, because the pressure of the atmosphere will raise or suspend the fluid so high, when the tube is exhausted of air. This height is about 30 inches when the fluid is quicksilver, and about 34 feet when it is water; and so on for other fluids, according to the rarity of them.

To use the Siphon, in drawing off any fluid; immerse the shorter end A into the fluid, then suck or draw the air out by the other or lower end C, and the fluid will presently follow, and run out by the Siphon, from the vessel at A to the vessel at C; till such time as the surface of the fluid sink as low as the orifice at A, when the decanting will cease, and the Siphon will empty itself of the fluid, the whole of that which is in it running out at C. The principle upon which the Siphon acts, is this: when the tube is exhausted of air, the pressure of the atmosphere upon the surface of the fluid at D, forces it into the tube by the orifice at A, as in the barometer tube, and down the leg BC, if B is not above the surface at D more than 34 feet for water, or 30 inches for quicksilver, &c. Here, if the external leg of the Siphon terminate at E, on a horizontal level with the immersed end at A, or rather on a level with the water at D, the perpendicular pressures of the fluid in each leg, and of the external air, against each orisice, being alike in both, the fluid will be at rest in the Siphon, completely filling it, but without running or preponderating either way. But if the external end be the lower, terminating at C, then the fluid in this end being the heavier, or having more pressure, will preponderate and run out by the orifice at C; this would leave a vacuum at B but for the continual pressure of the atmosphere at D, which forces the fluid up by A to B, and so producing a continued motion of it through the tube, and a discharge or stream at C.

Instead of sucking out the air at C, another method is, first to fill the tube completely with the fluid, in an inverted position with the angle B downward; and, stopping the two orifices with the fingers, revert the tube again, and immerge the end A in the fluid; then take off the fingers, and immediately the stream commences from the end C.

Either of the two foregoing methods can be conveniently practised when the Siphon is small, and easily managed by the hand; as in decanting off liquors from casks, &c. But when the Siphon is very large, and many feet in height, as in exhausting water from a valley or pit, the following method is then recommended: Stop the orifice C, and, by means of an opening made in the top at B, fill the tube completely with water; then stop the opening at B with a plug, and open that at C; upon which the water will presently slow out at C, and | so continue till that at A is exhausted. And this method of conveying water over a hill, from one valley to another, is described by Hero, the chief author of any consequence upon this subject among the Ancients. But in this experiment it must be noted, that the effect will not be produced when the hill at B is more than 33 or 34 feet above the surface of the water at A.

In an experiment of this kind, it is even said the water in the legs, unless it be purged of its air, will not rest at a height of quite 30 feet above the water in the vessels; because air will extricate itself out of the water, and getting above the water in the legs, press it downward, so that its height will be less to balance the pressure of the atmosphere. But with very sine, or capillary tubes, the experiment will succeed to a height somewhat greater; because the attraction of the matter of the very fine tube will attract the fluid, and support it at some certain height, independent of the pressure of the atmosphere. For which reason also it is, that the experiment succeeds for small heights in the exhausted receiver; as has been tried both with water and mercury, by Desaguliers and many other philosophers. Exper. Philos. vol. 2, pa. 168.

The figure of the vessel may be varied at pleasure, provided the orifice C be but below the level of the surface of the water to be drawn up, but still the farther it is below it, the quicker will the fluid run off. And if, in the course of the efflux, the orifice A be drawn out of the fluid; all the liquor in the Siphon will issue out at the lower orifice C; that in the leg BC dragging, as it were, that in the shorter leg AB after it.

But if a filled Siphon be so disposed, as that both orifices, A and C, be in the same horizontal line; the fluid will remain pendant in each leg, how unequal soever the length of the legs may be. So that fluids in Siphons seem, as it were, to form one continued body; the heavier part descending like a chain, and drawing the lighter after it.

The Wirtemberg Siphon, is a very extraordinary machine, performing several things which the common Siphon will not reach. This Siphon was projected by Jordan Pelletier, and executed at the expence of prince Frederic Charles, administrator of Wirtemberg, by his mathematician Shahackard, who made each branch 20 feet long, and set them 18 feet apart; and the description of it was published by Reiselius, the duke's physician. This gave occasion to Papin to invent another, which performed the same things, and is described in the Philos. Trans. vol. 14, or Abr. vol. 1. Reiseline, in another paper in the same volume, ingenuously owns that this is the same with the Wirtemberg Siphon.

In this engine, though the legs be on the same level, yet the water rises up the one, and descends through the other: The water rises even through the aperture if the less leg be only half immerged in water: The Siphon has its effect after continuing dry a long time: Either of the apertures being opened, the other remaining shut for a whole day, and then opened, the water flows out as usual: Lastly, the water rises and falls indifferently through either leg.

Musschenbroek, in accounting for the operation of this Siphon, observes that no discharge could be made by it, unless the water applied to either leg cause the one to be shorter, and the other longer by its own weight. Introd. ad Phil. Nat. tom. 2, pa. 853, ed. 4to. 1762.