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.
Nitrophenyl pentadienal solution of naphthoresorcinol is added to a swab of the item in question and then concentrated hydrochloric acid is added. The observation of a red color indicates a positive test. Napthoresorcinol was frequently used in early organic chemistry investigations to determine the presence of aldehyde groups in solution, a red adduct is formed in acidic solution. Nitrophenyl pentadienal Nitrophenyl pentadienal, nitrophenylpentadienal, NPPD, or METKA (Russian for "mark") colloquially known as "spy dust", is a chemical compound used as a tagging agent by the KGB during the Cold War Soviet Era. Soviet authorities in Moscow tracked Americans by applying an almost