Soldering to mercury switch


Richard Parker
 

Does anyone know of any required techniques / potential issues with soldering to the legs of a mercury switch?

Many thanks for any advice.

Richard


Neville Michie
 

HI,
because mercury forms amalgams with many metals, it is likely that the
terminals of the mercury switch are brought through the glass with
tungsten wires, which has a good expansion match with borosilicate glass (Pyrex).

It is possible to hard solder to tungsten with zinc rich solders, but this is at
a high temperature.

In my memory (from 60 years ago) I remember a glass blower telling me that
tungsten can be soft soldered with a nitrite flux. I have never tried this.

If the leads come out of the glass in Dumet wire (a copper clad nickel iron alloy)
then the wire can be tinned by applying phosphoric acid (concentrated) to the cold wire,
then with a well tinned copper soldering iron, quickly tinning the wire.
If iron wire is heated more slowly with phosphoric acid, then a resistant film of iron phosphate forms
that prevents soldering.

The final method is to clean the wire and crimp a copper tube over it. This may be then soft soldered.

That is my full store of information that might help,
cheers,
Neville Michie

On 2 Jul 2021, at 09:52, Richard Parker <groupsio@neonsky.co.uk> wrote:


Does anyone know of any required techniques / potential issues with soldering to the legs of a mercury switch?

Many thanks for any advice.

Richard