Alan,

On Tue, 3 Jan 2006 13:20:48 -0000, Alan B. Pearce wrote:

> >> try Mercury.
> >
> >I did - tastes *awful*!  :-)
> 
> No fillings in your teeth then ... ;)

Plenty - that's what I meant...  :-)
 
>...
> But you can get relays with mercury wetted contacts for very low current
> applications.

Do you mean that mercury forms the contact?  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.  To switch on the tube was tilted towards the 
electodes, and the mecury ran down and shorted between them, to switch off it tilted the other way and the 
mercury ran away and uncovered the electrodes.  Is this what's known as "mercury wetted contacts"?  This was 
not a low current application!

> 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?

Cheers,


Howard Winter
St.Albans, England


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