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I accidentally fell down a deep rabbit hole while trying to figure out how pH meters work. I thought this would be a really nice simple example of a scientific instrument, suitable for didactic explanation as part of an exposition of the failures of logical positivism. FAIL
I mean how hard could it be to measure pH?
Turns out there are two (or more) types of meters that work on entirely different principles. That they are measuring the same thing depends on masses of theory and experimental confirmation that the user doesn’t know anything about.
Turns out there are two (or more) types of meters that work on entirely different principles. That they are measuring the same thing depends on masses of theory and experimental confirmation that the user doesn’t know anything about.
It appears to be literally true that no one knows how the better type works. They use a “glass electrode” that is semipermeable to hydrogen ions. The nature of the electrode is a closely-guarded trade secret and they appear to be discovered by trial and error, not theory.
pH meters are peevish as hell and give maliciously wrong readings unless you are extremely polite to them. You have to recalibrate them before every measurement in case they are in a bad mood.
I tapped out while trying to understand a long, vitriolic, hyper-technical argument about whether pH meters actually measure H+ (per the undergrad definition) or H3O+ (which is what you get in aqueous solution) and whether it matters.
Here’s an interesting thread from someone who actually knows what they are talking about (I assume):
