In chemistry, what do the letters “PA” stand for?

Dear Cecil:

What do the letters PA stand for? I know some, we'll say, amateur chemists who concoct all sorts of things and consistently have to check the PA to get it right. But none seems to know what PA stands for or why it's such an important factor. The makers of the "Strong Dope" have let me down, so I turn to you, the writer of the Straight Dope.

PS: Could you mail me a reply? I'd send you a stamp but I'm in jail awaiting transfer to the Texas Department of Corrections. If you can't, put it in the next book and I'll read it depending on which of us (the book or me) is out first.

Cecil replies:

Too bad about prison, Dunc, but I told you to get that census form in on time. I imagine what your friends are referring to is not PA but pH, a measure of the acidity or alkalinity of a solution. The pH scale ranges from 0 to 14, 0 being highly acidic, 14 highly alkaline, and 7 neutral. Maintaining a proper level of acidity is important in many chemical processes, and while my experience in home-brew drug manufacture is limited, I imagine it’s important there, too.

The pH scale was invented in 1909 by one S.P.L. Sorenson and stands for the exponential power (originally German Potenz) of hydrogen ion concentration. Hydrogen ions are the positively charged particles that make acids acidic. They like to mix it up with other molecules, so the more of them you have, the more potent the acid. For the record — I know this is going to sound like high school chemistry, but I feel obliged to be thorough — a pH of 1 means you’ve got 10-1 moles of hydrogen ions per liter, or one tenth of a mole; a pH of 14 means you’ve got 10-14 of a mole, or one hundred-trillionth. What’s a mole, you inquire? Science talk for “whole bunch of,” of course. Don’t ask silly questions.

Now we know why they call it the Texas Department of Corrections

Dear Cecil:

In reference to the question you answered from Mr. Duncan Staggs concerning what PA means, you are wrong. Mr. Staggs most likely is asking about PA as it relates to the manufacture of methamphetamine. PA stands for lead acetate. Trust me, I know.

Far be it from me to tell large gentlemen with weapons they’re mistaken about their terminology, but Dunc said his buds have to “consistently check the PA to get it right,” which sounds like the litmus-paper pH test. Also, the chemical notation for lead acetate is Pb(C2H3O2)2.3 H2O, not PA.

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