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Sterilising jewellery

G’day - here is another tuppence worth; Formaldehyde (HCHO) is a
powerful sterilizing agent. It is actually a gas, but is sold as a
40% solution in water. (as in fact, hydrochloric acid is similarly
made) A 5% solution of this formaldehyde should kill almost anything
including viruses. It is used extensively in the mortuary and
embalming industries, and is often used to sterilize surgical
instruments. The only really positive method of sterilization is to
place the item in a very strong sealed vessel with a little water, and
heat it until the steam is at a temperature of 121C for a period of
not less than 20 minutes. It is called ‘autoclaving’. This is
infallible if carried out properly.

When I was interested in bacteriology I needed to grow cultures, and
therefore had a need to start with completely sterile, bacteria free
equipment. I used a large domestic pressure cooker, and with each
batch, I included a little sealed glass capsule of pure benzoic acid
which melts at 121C, inside an item being sterilized. When the
pressure vessel was properly cooled, and opened at the end of the
cycle, one could examine the capsule and see that the benzoic acid
crystals had melted and re-solidified. It invariably had, and the
subsequent incubation at 34C of one of the items (a test tube or
petri dish) using sterile media, proved beyond all shadow of doubt
that everything was indeed sterile.

However, despite the fact that I literally breathed the stuff when I
was sampling formalin tanks then later sucking it up in pipettes at
the age of 17 - 20 and again 24 - 26 it is poisonous and shouldn’t be
inhaled or allowed to get on one’s skin!! OSH would have gone
orbital!! –

John Burgess; @John_Burgess2 of Mapua Nelson NZ