Homebrew_PCBs

grantfair2001 wrote:

> Thanks again, Adam-
>
> I found an inexpensive balance made in India for C$15 and it is
> remarkably sensitive, comparing the weights included against those of
> Canadian coins, whose weight is listed by the mint on the web.

That's a good idea. I'm sure a new coin would be much better than
+-1% accurate.
If you are buying lab stuff get a eye dropper bottle (the ones
with the dropper fixed to a screw top lid) and also a normal eye
dropper. Make up 1 liter of about 0.002% pH indicator in clean
bottle using DI water. Put the standard 1.0 Molar NaOH solution
in the dropper bottle. Take 10 drops of etchant into a rinsed
glass (using the normal eye dropper), then add about 10 ~ 20 ml
of the pH indicator. Whilst stirring carefully add drop by drop
the 1.0M NaOH until color changes. Each drop represents 0.10M of
free acid in the etchant. Having separate dropper for each
solution means there is little to clean up. That should make acid
analysis a piece of cake.

If you have a burette then of course use that because its much
more accurate ?

>
> I also found an inexpensive source of indicators in the US who will
> send them up here.

What indicators are you getting ?

>
> After 12 hours with the airstone I don't see any change in etchant
> color. The ph was still at 3 today so I added the bit of HCl left in
> the 4 litre jug.

I would imagine the dark color of this solution would make pH
papers useless.