Instruments
pH Meter
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A pH meter is an electric device that measures the acidity or alkalinity of a solution, consisting of a voltmeter attached to a pH-responsive glass electrode and a reference electrode. Arnold O. Beckman built the first practical pH meter in 1934 at Caltech, at the request of a citrus-industry chemist who needed a reliable way to measure the acidity of lemon juice, and went on to found the company that became Beckman Instruments to manufacture it.
Facts
Invented YearSourced to the subject's own account MeasuresThe concentration (activity) of hydrogen ions in a solution, expressed on the pH scale. 2 Operating PrincipleA glass electrode sensitive to hydrogen-ion activity develops a voltage relative to a stable reference electrode; the meter converts that voltage to a pH value using the Nernst equation, in which one pH unit corresponds to about a 59 millivolt change at 25 degrees Celsius. 2 Operating RangeThe standard pH scale runs from 0 to 14, with 7 as neutral. 2 Open Questions
ResolutionNot stated in the cited source. 2 Commodity portable meters are commonly built to 0.01 pH units, but that figure was not confirmed in this specific source, so it is not written here as attested. Cross-Tradition Connections
Invented By
Patented the pH meter, originally called an acidimeter, in October 1934, then founded the company that became Beckman Instruments to sell it.
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