abbr 1  pharmacopoeia  2  phosphor  3  phot .
n :  a measure of acidity and alkalinity of a solution that is a number on a scale on which a value of 7 represents neutrality and lower numbers indicate increasing acidity and higher numbers increasing alkalinity and on which each unit of change represents a tenfold change in acidity or alkalinity and that is the negative logarithm of the effective hydrogen-ion concentration or hydrogen-ion activity in gram equivalents per liter of the solution <instead of saying that the concentration of hydrogen ion in pure water is 1.00 x 10^-7, it is customary to say that the of pure water is 7 -Linus Pauling>  : also  :  the condition represented by such a number - compare PK  .
 
 
 
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