A pH meter measures a pH or the acidity/alkalinity of substances. Usually, pH meters need to be calibrated every day or week.

When Arnold Beckman, a professor of analytical chemistry at the California Institute of Technology, was asked to devise a way to measure acidity in citrus fruit, the resulting “acidometer” ...

Understanding the nature of pH has bedeviled beginning (and not-so-beginning) chemistry students for nearly as long as chemistry has had students. It all seems so arbitrary, being the base-10 log ...