The dental casting machines tend to be pretty limited in terms of
the size of crucible and flask they can handle. Rings,
(one-per-flask) are probably about all you’ll have the room for. If
you’re lucky, he had a jewelry machine, and just used small flasks,
but the odds of that are low. How big is it? Does the flask end pivot
with an elbow joint? (So that the flask end swings to about 90
degrees relative to the angle of the main arm.) If it has an elbow,
you may have a jewelry sized machine. (may, just may) If it’s solid,
it’s probably a dedicated dental machine, and rings are pretty much
Crucibles may be an issue. I’d call one of the larger suppliers, and
see if they can help you. Pictures emailed to whomever you end up
talking to will probably be key.
As far as the gas bottle goes, it’s either acetylene or propane. You
can’t switch. Acetylene tanks are sort of skinny and built like,
well, tanks. Propane tanks look like (and often are) BBQ grill tanks.
(in the US, they’re often white.) Take the tank to the local
industrial gas supplier (in phonebook under “welding supplies”), and
they can tell you what the tank is, and what you can do with it.
Hope this helps,