Reg Edwards wrote:
Way back in the 1970's I visited the National Physical Laboratory (NPL) at
Teddington, West London.

I was priviledged to see, but not to touch, the National Standards of the
Ohm and of the Volt. There were a number of 4-terminal resistors submerged
in a temperature-controlled oil bath. There was about a dozen Western Cells

Is that something like a Weston Cell?

On a serious note, don't overlook refrigeration oils, they are high
quality, light, dry oils for immersed motor windings, and available in
smaller sealed tins (around 5 litres).

Owen