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KHP is slightly acidic, and it is often used as a primary standard for acid–base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic . [ 4 ] [ 5 ] [ 6 ] It is also used as a primary standard for calibrating pH meters because, besides the properties just mentioned, its pH in solution is very ...
A primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are used to calibrate other standards referred to as working standards. [1] [2] See Hierarchy of Standards.
Examples of primary time, (i.e., frequency standards) are caesium standards and hydrogen masers. The international second is based on the microwave frequency (9,192,631,770 Hz) associated with the atomic resonance of the hyperfine ground state levels of the caesium-133 atom in a magnetically neutral environment.
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At its annual convention at Dallas, TX, the NFPA formally adopted a standard with 2 + 1 ⁄ 2-inch hose with 7.5 threads per inch as the primary standard, with additional sizes of 3 and 3.5 inches (each with 6 threads per inch) and a 4.5 inch coupling with 4 threads per inch, with the fire hydrant standard specifying one 4.5 inch port and two 2 ...
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