Homebrew PCBs

At 10:34 am ((PDT)) Thu Apr 12, 2007, Stefan Trethan wrote:

>On Thu, 12 Apr 2007 01:16:35 +0200, Len Warner <novost@...> wrote:
>
> > It is more hazardous in handling than hydrochloric acid:
> > because it not volatile - so un-neutralized splashes get
> > more concentrated as they dry, rather than evaporating;


>Will it really concentrate? Sulphuric acid is very hygroscopic,
>should it not absorb moisture from the air?

Conc. sulphuric acid is a powerful dessicating agent and would
absorb atmospheric moisture.

If you splash conc. sulphuric acid onto organic matter it will
dehydrate it quickly  - viz. the sugar/sulphuric acid carbon volcano
demonstration. So handle conc. sulphuric with great care and as
little as possible.

I meant working-strength dilution. Dilute sulphuric acid will lose
water vapour and will not evaporate much H2SO4 until the
concentration rises to around 77% - which strength is not
something you would like to leave laying around the place and
may be higher than the concentration you are bought it at!

Whereas conc. hydrochloric acid starts at around 35% and
when spilled will evaporate completely, though not necessarily
without causing some damage; sulphuric acid, diluted to a
similar strength to make it easier to handle, when spilled will
linger and strengthen and so be likely to cause "acid burn" stains
and possibly start actual fires (as oxidizing oil does in old rags).

So protect against splashes, wear synthetic clothing, and
wash down all contaminated surfaces well then neutralize with
sodium bicarbonate (or carbonate) solution. (Or, if you want
minimum residues and don't mind the smell, ammonia water.)


Regards, LenW