A crucible is simply a small heat-resistant pot with a lid, often made of
porcelain, which is used for heating solid mixtures.
Heating any oxidisible material with potassium nitrate could be rather
dangerous. (As you no doubt know, gunpowder is a mix of potassium
nitrate, charcoal and sulphur.) You would need to ensure that the initial
combustion step was fully completed.
Assuming you got this done without mishap it would probably be possible
to produce silver nitrate that was useable in salt prints - as you know
from your reading a lot of photographers used to do this. However a lot
of photographers used to do some much more dangerous chemistry - and
probably a reasonable proportion of them died from it either
spectacularly in a few cases or insidiously in the main.
Personally I would get rid of it in small quantities mixed in with normal
waste. A few years ago I had some radio-active material to dispose of,
spent a long time phoning round various officials and readiing all sorts
of inpenetrable safety documents until finally I got to the real
authority who told me that if the total amount was less than a certain
amount the recommended method of disposal was to put it togther with
other materials in a normal dustbin.
Peter
petermarshall@cix.compulink.co.uk