252 THE SIPHON. 



then closed with the finger and the longer branch filled. When the 

 tube is full, both ends are closed with the fingers, the tube is in- 

 verted, the longer branch dipped into water, the finger withdrawn 

 from that end, and the tube clamped in the retort-stand, so that the 

 end of the shorter branch is somewhat lower than the surface of the 

 liquid ; the finger is then withdrawn from the other end also. Water 

 will run out from that end, but it will cease to flow when the surface 

 at a has sunk to d ; if the aperture is horizontal, the water remains 

 within the tube. If now the tube be lowered in the retort-stand, 

 the flow of water commences again ; but if d be raised ever so little 

 above a, the water flows back into the vessel. 



The vessel which contains the water may also be placed near the 

 edge of a table so that d projects beyond it, and the tube may be filled 

 by simply applying the lips at the end d and sucking ; the pressure 

 of the air in the tube is diminished by suction, and the external pres- 

 sure drives the water into the tube. 



A tube, bent as shown in fig, 171, and used for 

 transferring a liquid over the sides of vessels, or any 

 other small elevation, is called a siphon. Its shape 

 often resembles a U or V, and the two branches may 

 be of equal or different lengths. If a liquid is to be 

 completely removed from a vessel, the longer branch 

 of the siphon must be outside the vessel, for only 

 in this case the end of the external branch will be to 

 the last below the surface of the liquid. The height 

 to which a liquid can be raised by a siphon depends 

 on the specific gravity of the liquid. The pressure of 

 the air supports a column of water nearly 10 m high ; 

 hence the highest point of a siphon used for trans- 

 ferring water must not be more than 10 m above the 

 surface of the water. A longer siphon could not be 

 filled by suction, and if filled by other means it would 

 not act, for when the instrument is inverted, the water 

 would immediately leave the highest portion, and fall 

 until in both branches the column had a height of 10 m 

 only; this is shown in fig. 172. Water may thus be 



