Yesterday Mr. Grace discussed the open mercury switches used in Welte
products.  In these instruments, contact is made by plunging a rod into
a little cast iron cup containing a pool of mercury, with a bit of oil
floated on the surface to prevent oxidation or evaporation.

In all the rebuilt orchestrions that I have seen, these switches have
been replaced or paralleled with some modern mechanical switches, for
the obvious reasons stated.

I see absolutely nothing wrong with using the solid state replacements
system he describes.  It is essential since he requires a modern
controllable DC power supply to get the two levels of DC required for
the original Welte-Mignon motor.

But I worry about replacing the mercury in the cup with powdered
graphite.  Once the instrument is rebuilt, there may be puffs of
air moving around inside the case.  In any case, the graphite will
gradually blow around, and get on anything located nearby, leaving a
greasy film that is hard to clean up.  Anyone who has spilled even a
tiny amount of graphite knows how much of a mess it makes.

I see nothing wrong with adding a microswitch, or a shutter and
LED/photoswitch to trigger the solid state relay, in parallel with
the existing switch cup.

But for those who want authenticity, there are modern eutectic liquid
alloys made to replace mercury in open switches, without the hazards
associated with mercury.  They are based on gallium and indium alloyed
with tin, copper, and zinc or bismuth, melting at -11 deg. C.  They are
made by NewMerc alloys:

  http://www.reade.com/Products/Alloys/newmerc.html

Richard Vance

 [ No matter what the type of motor, I recommend that a 130-volt
 [ varistor (or 260-volt, for 220-240 VAC mains) be wired in
 [ parallel with the motor.  The varistor will then dissipate
 [ the residual energy stored in the motor field, thus preventing
 [ damage to the switch and the motor.  The varistor energy rating
 [ is specified in Joules (same as watt-seconds), which should be
 [ at least equal to the watt-seconds energy "kicked back" by the
 [ motor if the switch is opened when starting.  -- Robbie