pH
The 0-to-14 scale measuring how acidic or basic a solution is — 0 is strongly acidic, 14 is strongly basic, 7 (pure water) is neutral.
Origin
Coined by Danish chemist Søren Sørensen in 1909 while working on beer brewing at Carlsberg. The 'p' is debated — possibly the German potenz ('power'), Latin pondus ('weight'), or just an algebraic placeholder; the H is for hydrogen ion concentration. The scale is logarithmic: pH 4 is ten times more acidic than pH 5, a hundred times more than pH 6. Vinegar is around 2.5; blood is tightly regulated to 7.35–7.45; bleach is around 12.5.
Modern usage
'Acidic' as a metaphor for caustic or critical (a thread, a comment, a personality) is heavily used online — 'acidic Twitter take.' Skincare and beauty marketing leans on pH constantly (the 'pH balanced' label). Pool chemistry, gardening, and brewing all use the scale literally.
In the wild
Her review of the album was extremely acidic.— common usage
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