[alt-photo] Re: On working with hydrochloric acid

[etienne garbaux]

Francis wrote:

>I've been re-acidifying FAEW hot press with distilled white vinegar.
>I  haven't used (but am considering using) pH paper strips to
>monitor the acidity since its hard to see any bubbles in solution
>in my dim room.

Or, you could do it real old-school style -- dip your finger into the 
bath and touch it to your tongue.  Of course, DO NOT do this if you 
have reason to believe anything toxic may have been solubilized, for 
example, if the bath is a clearing bath after any dichromated or 
heavy metal process, or you have reason to believe the paper has 
anything significantly toxic in it.

Since the paper needs to be at least washed, and probably 
substantially if not fully dried (or do you coat right out of the 
rinse with the paper fully wet, just squeegeed?), why do it in a dim 
room to begin with?  Please note that I'm not disparaging the use of 
real measurement tools -- I myself use a cheap portable pH meter for 
such things -- just asking.  And vinegar is weak enough that it 
doesn't effervesce very dramatically, anyway, particularly as the 
reaction nears completion, so you need to leave the paper in active 
vinegar for at least 2 or 3 if not 5 or 10 times as long as you see 
bubbles in any event.  (This is true even for more active acids at 
the relatively low concentrations we use in alt processing.)

Best regards,

etienne