dangerous amateur - 27-4-2012 at 03:01
Hi there,
what's your experience/knowledge about that?
I've got a pack of original Merck Strips 1-14 here, only I know they are from the early nineties. The seem to work though.
And another question:
There are these plastik strips, like mine, where the indicator stuff is glued to.
And then there is this paper stuff that comes on spools.
What do you prefer? Which one is used in what situation?
gutter_ca - 27-4-2012 at 08:01
Usually, the plastic ones are "no bleed." I would use these if testing pH of something I planned to use that needed to be pure.
BromicAcid - 27-4-2012 at 08:15
I love the strip paper but it is less accurate for shoulder pH ranges. To tell a 2 from a 3 or a 4 can sometimes be a challenge. The plastic ones
are better for this and give a more accurate range however they are susceptible to oxidizing conditions as well as solutions that are not colorless or
white. If your solution were black for example you could look at the bleeding edge of a piece of pH paper but on the plastic strips a square that is
supposed to be light colored might be indecipherable. Going back to oxidizing solutions I have seen the plastic strips give contradictory values on
the strip itself due to some of the components loosing their chromophore.
dangerous amateur - 27-4-2012 at 12:02
Thank you for sharing your experience.
OK, I'll get a new package of the plastic ones.
GreenD - 27-4-2012 at 12:44
just tried my old school "blue ph paper" for qualitative acidity - it is about 5 years old and still works.
Arthur Dent - 28-4-2012 at 10:27
I have what can be referred as "antique" pH paper which dates (I kid you not) from the mid to late 70's... Some Blue Litmus paper (Sidam brand) Red
litmus paper from Fisher scientific, and "Alkacid" Test Paper also from Fisher Scientific. Actually, the Blue Litmus paper looks more like it's from
the late 50's just by the label on the bottle and the cork stopper on top ! 
None of the paper strips seem to have lost their potency, and I use them occasionally to have a rough ballpark idea of the PH of a solution, my cool
new pH meter taking care of the more precise readings. After a few tests with the new pH meter, it seems relatively accurate so i use it most of the
time now.
Robert