grantfair2001 wrote:
>
> Hi Adam -
>
> An automated process would take the tedium and time out of it. But do
> you know of sensors up to the job? A SG sensor might not be too hard
> to improvise. But molarity?
A simple float might be done with a block of polyethylene plastic with a
small stone tied to it somehow. But the S.G is fairly slow changing and
doesn't require frequent measurement so using hydrometer will not be a
problem, and you know its accurate. The hydrometer will be essential
when mixing/making your first batch of etchant.
Acid molarity is best done by titration. You don't need indicator since
your end point is the first signs of the copper precipitate. In fact
one of the technical staff at
http://www.oxfordvue.com told me in a
email that titration of copper chloride etchant should only be done
using the copper hydroxide precipitate for end point detection. He said
the high copper levels interfere with pH and causes most indicators not
to work. I tried eye dropper method but the drop size of etchant is
about 1.5 times volume that of sodium hydroxide. Counting drops is very
inaccurate. Instead I use a 1.0 cm^3 measuring pipette and a pipette
sucker. Take 1.0 mil of etchant into about 20 cm^3 tap water, then
titrate with 1M NaOH solution, until I see first signs of precipitate.
Note that towards the end point the solution must be mixed and the NaOH
added slowly so make sure all the acid has reacted. I sometimes heat in
a microwave oven for a few seconds before doing the titration to speed
up the reaction of last traces of acid towards the end point.
Glass measuring pipettes and the suckers are about $2 to $3. The problem
is only lab supplies have this kind of stuff.