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'[OT] Mercury, was Re: Comments on keypad design?'
2006\01\03@094525 by Alan B. Pearce

face picon face
Figured that we better change the tag if we're going to talk like this ...

>> >> try Mercury.
>> >
>> >I did - tastes *awful*!  :-)
>>
>> No fillings in your teeth then ... ;)
>
>Plenty - that's what I meant...  :-)

Oh, yeah, know that feeling. Don't remind me, I have one that needs
repairing.

>...
> But you can get relays with mercury wetted contacts for very low current
> applications.

Do you mean that mercury forms the contact?

I don't know precisely how they work, except that the mercury somehow
performs the function of the "wetting current" that was mentioned earlier on
in this thread.

>I remember one house we lived in many years ago had a relay
>which switched the storage-heater supply under control of a
>timeswitch, and it consisted of a horizontal glass tube with
>two electrodes at one end and with a blob of mercury in it.
...
>Is this what's known as "mercury wetted contacts"?  This was
>not a low current application!

Hmm, that is what I know as a mercury tilt switch. Similar things have been
used in telephone handsets on speaker phones and the like to switch off the
microphone when dialling with the handset in place, but the speaker on. I do
not know what the actual construction of a mercury wetted relay is, but it
may be that they do a similar thing.


>> Anyone that thinks gold contacts do not corrode or get dirty
>> should talk to telephone engineers in geothermal regions. I
>> know the telephone exchange in Rotorua, NZ, went to extraordinary
>> lengths to keep the sulphurous air out of the exchange back in
>> the days of using relays. The area around Rotorua is very
>> similar to Yellowstone Park in the USA.
>
>Presumably if you need a telephone exchange it means that
>people live there, in this sulphurous atmosphere?

Err, yeah, like a city full - which is minimum 20,000 in NZ, plus the
surrounding environs. Constant rotten eggs smell, but nice hot pools.

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