Chap. 6.]

Ewbank’s Siphons.

527

equals the capacity of the siphon. To use this instrument, fill the widetube with water or some other fluid, and place the short leg into the liquidto be decanted ; then close the orifice of the long'leg with the finger, andraise the moveable tube (by the ring attached to it) and the siphon willbe charged. In using this instrument, the fluid by which it is chargeddoes not mix with that which is decanted, as in No. 260. The apparatusis more simple than a syringe and is not liable to be deranged. By usingmercury both the length and bore of the charging tubes may be greatlyreduced. As these tubes themselves constitute a siphon, (see No. 238,)the upper end of the small exhausting one should extend a little abovethat which contains the charging fluid, lest this should occasionally riseover the orifice—in which case the whole would be drawn off. A descrip-tion of this siphon was published in the Journal of the Franklin Institutefor November, 1834.

No. 265,

No. 266.

No. 264.

No. 267.

Nos. 265-6 represent another mode of charging siphons on the sameprinciple, but the apparatus is more simple and is accompanied with somepeculiar advantages. The siphon itself has no exhausting pipe attachedto it, but is a bent tube simply. It is put in Operation by means of amoveable tube of about the same length as the discharging leg, and havingthe bottom closed and a lip or spout formed on its upper edge. Thistubulär vessel is filled with water (or other fluid) and the long leg of thesiphon inserted into it. The short leg is then placed into the liquid to bedecanted and the moveable tube drawn gently down. The air withinbecomes rarefied and the instrument charged in consequence of the vacuityleft.in the long leg by the receding liquid. The moveable tube may thenbe wholly withdrawn or not as circumstances may dictate. If the liquidis to be decanted at intervals, or the stream increased or diminished, thetube should be used ; thus, to lessen or stop the discharge, slide up thetube and as the lip approaches to a level with the surface in the reservoirthe stream will become less and less, and by raising it still higher, as inNo. 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 gwage , viz. by accurately indi-cating the surface of the fluid within anv 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; allthat is required is to slide up the tube tili the liquid barely drops from thelip—its surface in the tube will then be on the same level as in the demi-john. If the moveable tube be made of glass, the quantity left can alwaysbe 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