The discussion on the railway site was generating other discussions regarding these strange resistors ...

• On the subject of salt pot variable resistances I knew of one theatre lighting installation using salt pot dimmers. The electrolyte in these would be boiling merrily by the end of the first act and the following interval was used for topping the pots up with water.

• I seem to remember from a visit to [a utility] that the electrolyte there was caustic soda, as it took more punishment before throwing itself all over the operatives present. Theatres used salt because they were less careful and boiling caustic soda descending from the heights onto the cast was marginally less desirable from a compensation angle.

Certainly a noval electrical device! [Linked Image]