The term "sour" has something to do with the so-called pH value: pH stands for pondus Hydrogenii, which means "weight of hydrogen", i.e. the concentration of hydrogen ions in a solution. The pH value therefore indicates how acidic (sour) or basic a solution is, with the most commonly measured values ranging from around 0 to 14. How the value is calculated, how its being tested and what it means exactly is explained in this article.
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