Litmus test (politics) Litmus test (politics) A litmus test is a question asked of a potential candidate for high office, the answer to which would determine whether the nominating official would proceed with the appointment or nomination. The expression is a metaphor based on the litmus test in chemistry, in which one is able to test the general acidity of a substance, but not its exact pH. Those who must approve a nominee, such as a justice of the Supreme Court of the United States, may also be said to apply a litmus test to determine whether the nominee will receive their vote.
Acidity function is uncommon. Hammett-type acidity functions are defined in terms of a buffered medium containing a weak base B and its conjugate acid BH: where p"K" is the dissociation constant of BH. They were originally measured by using nitroanilines as weak bases or acid-base indicators and by measuring the concentrations of the protonated and unprotonated forms with UV-visible spectroscopy. Other spectroscopic methods, such as NMR, may also be used. The function "H" is defined similarly for strong bases: Here BH is a weak acid used as an acid-base indicator, and B is its conjugate base. In dilute aqueous solution, the predominant