Siphons, Revisited

The siphon is a very useful example of early technology, the operation of which has long been well understood. A recent article1 makes the claim that established beliefs regarding this device are incorrect and proposes a “chain model” in which intermolecular forces within the fluid play a large role while atmospheric pressure does not. We have carefully tested, and disproved, this claim using four simple experiments employing inexpensive, easily available apparatus. We complement the experiments with a discussion of conceptual issues related to the device and by invoking earlier studies and observations.2–8 Our findings fully support an explanation based on Bernoulli's equation in which both gravity and pressure play important roles, but intermolecular forces do not.