Mercury Cup

A cup of iron, wood or some material that does not amalgamate or is unattacked by mercury, which is filled with mercury and made an electrode of a circuit. By dipping the other terminal of the circuit into the mercury a very good contact is obtained. It is well to cover the mercury with alcohol. The cup may be filled so that the mercury rises in a meniscus or semi-globule above its edges. For some purposes this form is useful, as for contacts with the end of a swinging wire or pendulum, because in such cases the contact can be made without the contact point entering the cup. The point swings through the projecting meniscus without touching the edges of the cup. A mercury cup and contact constitute a mercury break.