Liquid Dimmers (1915 - 1945)
Strand

Liquid Dimmer

Glazed earthenware jars, complete with fixed & moving lead cones.
(Made by a number of companies, not just Strand)

Also known as salt water dimmers and electrolytic dimmers.
Liquid dimmers can be used on DC or AC supplies.
The power supply is connected to two contacts in each dimmer. There's a fixed connection at the bottom the the dimmer jar, and a moving contact connected (via an insulator) to a steel wire which is moved by the control system (via pulleys). The distance between the contacts affects the voltage passed to the load (lantern). When the contacts are closest together (touching), maximum voltage is passed. As the contacts are moved apart, the amount of resistance increases, as more and more salt water is between them. At the lowest dimmer output, the water is taking on the energy of almost all of the voltage, and can even start to boil. The water must be topped up regularly.
The concentration of electrolytes in the water can be changed to enable the dimmer to be used on a range of diffferent loads. The salts are provided by washing soda crystals.

The last electrolytic dimmers were replaced in London in 1959.

Additional information:
(From Richard Havard) The Lyceum Theatre in Newport had a Strand Board which was removed when the theatre closed and "rebuilt" with original components in the Little Theatre in Dock St. Newport. There were 3 liquid master dimmers, that had been re used, in a locked cabinet on the fly floor in 1965. Later the theatre, which was a converted church, was demolished and a new shopping centre built which included a new Little Theatre, now called The Dolman Theatre after the chairman who masterminded the deal which allowed the developers to proceed and the Theatre Company have a purpose built theatre as part of the development!
(From Robin Childs) My old chief LX - Laurie Upton- was, as a boy responsible for topping up the brine dimmers at the theatre Royal in Portsmouth (probably around 1925) He told a story of the horrible stench during a dimly lit Shakespeare play - the pots would simmer and a rat had fallen in - eventually they found a complete skeleton boiled clean !!