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Nitric Acid - some safety suggestions


#1

Nitric acid is usually sold in concentrated form as a liquid, which
is extremely corrosive, very poisonous, constantly gives off acid
corrosive fumes, and in contact with many metals such as silver or
copper gives off a brown gas called nitric oxide which is also very
poisonous. Under the action of light it slowly decomposes into oxides
of nitrogen plus some free oxygen, and may thus produce a pressure in
a stoppered container. If kept for any time, the stopper should be
occasionally loosened (Carefully!) to avoid pressure build up.

It will cause burns in contact with human skin, so if nitric acid
contacts the body it should be flooded with a copious stream of cold
water. Spills should be covered with a thick layer of solid sodium
bicarbonate, which after no further bubbling is seen, may be swept
up and preferably scattered over the ground and covered with a layer
of soil, where it will do no further harm, having become a
fertilizer; sodium nitrate. Do not pour acid down the toilet or a
drain. Do not use newspaper or paper towels to mop up spills; it is
possible they may spontaneously catch fire. Mopping up spills with
sawdust is similarly dangerous.

Concentrated nitric acid should be kept in a dark place in glass,
polythene or polypropylene bottles, either glass stoppered or
stoppered with proper plastic (polythene) stoppers made for the
purpose. It will rapidly destroy corks and rubber bungs. Plastic
containers must be strong and rigid, not at all like the plastic milk
or soft drink bottles. It is safest to wear a proper respirator
designed to protect against acid gases and fumes and to wear plastic,
not rubber protective gloves; a plastic apron is a good idea too, as
nitric acid quickly rots clothing. Protective eyewear is essential.

When diluting concentrated nitric acid, it is necessary to perform
the operation in a well ventilated place, or in the open. Pour
over half of the water needed into a plastic or glass container, then
add the acid slowly with constant stirring, using a glass rod or
piece of stiff plastic - even lucite. A little heat may be
generated, but insufficient to produce boiling or spurting. Finally
add the rest of the water and stir well and stopper. Try not to
re-use bottles which have contained food items., and store well away
from children.

It is most important to label everything, and even more important
when poisons or corrosive materials are concerned. The acid will
slowly destroy paper labels, but covering paper labels with
transparent, adhesive polythene tape will help preserve them. Black
Marker Pen can be used with very bold, clear lettering and will
survive for quite a while, though colours will fade more quickly.
Pour out the acid in such a way that the inevitable drips will not
contact the label, and wipe the bottle carefully with a damp cloth
after re-stoppering.

Finally, having said all that scary stuff, bear in mind that one of
my first jobs as a lab boy at age 14 was to dilute strong acids in
five gallon quantities at a time, and to keep the hundreds of
laboratory reagent bottles all topped up every morning. They weren’t
concerned with safety in those days, so we got no protective
clothing, etc. Other than the raggedy lab coats departing students
left behind. Didn’t I ever have accidents? Of course I did,
but I’m now nearly 81. If you are lucky you draw a pension as a
prize for surviving.

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