Potassium dichromate, reaction with ethyl alcohol

The first instruments used by police to determine BrAc were developed in the 1930s. Until about 1980, the standard method involved adding K O , which reacts chemically with ethyl alcohol. Potassium dichromate has a bright orange-red color, whose intensity fades as reaction occurs. The extent of the color change is a measure of the amount of alcohol present. 

Hofmann appointed the seventeen-year-old Perkin as his personal assistant and guided him to work on the synthesis of the antimalarial drug quinine. Perkin had his own ideas for the synthesis of quinine and pursued them in his lab at his parents home. During Easter break 1856 Perkin ran a reaction with aniline (a compound derived from coal tar) and potassium dichromate that produced a black sludge. Dissolving the sludge in ethyl alcohol, Perkin found that the solution took on an intense purple color. Instead of synthesizing quinine, Perkin had made the first synthetic dye derived from coal tar mauve. 

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