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Persulphates


#1

G’day; somebody mentioned using sodium and ammonium persulphates.
(I inadvertedly lost the original mailing; I’m not ‘with it’ all the
time) and I felt that I had to offer my comment.

Well, the persulphates can be a bit unstable. They contain twice as
much oxygen as the sulphates and bisulphates; those who even partly
understand chemical formulae can doubtless understand why they could
be a problem to use. Their generic formula is X2S2O8 and X can be
sodium, potassium, ammonium,etc.,or hydrogen, which is the acid form
Compare this with sulphuric acid which has the chemical formula of
H2SO4 (which most people know about).

You will see that all the persulphates contain 8 atoms of oxygen as
compared to 4 in the sulphates, and it is this double amount of
oxygen which can cause problems. To the extent that some metal
persulphates when heated can explode with very great violence.
They are all very powerful oxidizing agents due to that extra amount
of oxygen in their make up.

If they happen to come into contact with organic substances (that
is, any substance containing carbon, other than the carbonates) the
extra oxygen can oxidize such things to the point of spontaneous
combustion and explosion - which after all, is very rapid combustion.
Oxygen plus organic carbon compounds combine and generate heat when
activated by outside heat; which is why most of them burn in the
atmosphere. (Baby, light my fire)

So my suggestion is to not tangle with the persulphates unless you
know exactly what you are doing and why, and what precautions to
take.

As a footnote to this, I experienced an extremely violent
persulphate explosion which took out an entire small senior student
laboratory in a university and injured a couple of students, who, of
course, were merely bystanders, minding their own business. Luckily
for me, I was in my nearby office and was able to field the
casualties and to render a bit of first aid as they reeled,
profoundly shocked out of the lab doorway. The real perpetrator had
left his experiment and was on another floor.

The silliest thing was, at the subsequent ‘inquest’, his research
supervisor assured us that the compound his student was using was
"inherently safe".

It just goes to show, don’t it?

Cheers for now,
John Burgess; @John_Burgess2 of Mapua Nelson NZ