The New Student's Reference Work/Siphon

Siphon (sī′fŏn), an instrument for transferring liquid from a vessel at one level to another at a lower level.

FIG. 1

The simplest possible form is shown in the accompanying figure, where the liquid A is being emptied into the vessel D. In order to start a siphon the pressure of the air must be diminished in the branch C D. The pressure of the atmosphere on the surface B then forces the liquid up the arm A C, and, in flowing down the arm C D, this liquid acts as a pump and keeps the pressure in C D below that of the atmosphere. Evidently, however, this pumping must cease as soon as the liquid in the vessel D rises to the same level as the surface B. It is also clear that, since the water is driven up into the arm A C by means of the earth's atmosphere, no siphon will work in a vacuum.

FIG. 2

The safest and most convenient form of siphon, especially for transferring acids is that shown in figure 2, which is provided with a mouthpiece for starting, but without danger of getting acid or poison into the mouth. The action will be evident from the figure.