Siphon - History

History

Egyptian reliefs from 1500 BC depict siphons used to extract liquids from large storage jars.

There is physical evidence for the use of siphons by Greek engineers in the 3rd century BC at Pergamon.

Hero of Alexandria wrote extensively about siphons in the treatise Pneumatica.

In the 9th century, the Banu Musa brothers invented a double-concentric siphon, which they described in their Book of Ingenious Devices. The edition edited by Hill includes an Analysis of the double-concentric siphon.

Siphons were studied further in the 17th century, in the context of suction pumps (and the recently developed vacuum pumps), particularly with an eye to understanding the maximum height of pumps (and siphons) and the apparent vacuum at the top of early barometers. This was initially explained by Galileo Galilei via the theory of horror vacui ("nature abhors a vacuum"), which dates to Aristotle, and which Galileo restated as resintenza del vacuo, but this was subsequently disproved by later workers, notably Evangelista Torricelli and Blaise Pascal – see barometer: history.

Specifically, Pascal demonstrated that siphons work via atmospheric pressure (as Torricelli had advocated), not via horror vacui, via the following experiment. Two beakers of mercury are placed in a large container, at different heights. The beakers are connected with a three-way tube: a regular siphon (U-shaped tube), with an additional tube extending upward from the hook in the tube: one end of the tube goes down into each beaker (as in a normal siphon), while the third end faces upward, and is open to the air. The large container is slowly filled with water (the tube remains open to the air): as water goes into the container, the weight of the water forces the mercury up into the tube (water being denser hence heavier than air) – as the water level increases, the level of mercury rises because the pressure increases – and once the mercury enters the top of the siphon, the mercury flows from the higher beaker to the lower, as in a standard siphon. As the mercury had been open to the air at all time, there was never a vacuum – it was instead the pressure of the water.