Hello listmembers

Has anyone got some useful tip to help me out when running nitrates. I'm
aiming for a beam size of around 1e-7 for mass 28, but after I've run a
small (sic 10-15 samples of 1mg each) batch, the silver wool is turned to
black gunge and I'm up for a new quartz tube and packing. I suspect there
is a moderate to high salt content which is the culprit.

My configuration is

quartz tube, plus silver wool (5g) plus CuO (40mm), plus CrO3 (25g). I tend
to reuse the CrO3 if my tube goes quickly, as I don't feel its been
exhausted, so at least have some savings there.

How can I put a 'reasonable' batch of nitrates through without loosing my
tube too early. Is it possible? Should I try a different packing? Should I
put in more silver wool ie 10g?

thanks for your help

Karyne