<P> The Kastle--Meyer test is a presumptive blood test, first described in 1903, in which the chemical indicator phenolphthalein is used to detect the possible presence of hemoglobin . It relies on the peroxidase - like activity of hemoglobin in blood to catalyze the oxidation of phenolphthalin (the colorless reduced form of phenolphthalein) into phenolphthalein, which is visible as a bright pink color . The Kastle--Meyer test is a form of catalytic blood test, one of the two main classes of forensic tests commonly employed by crime labs in the chemical identification of blood . The other class of tests used for this purpose are microcrystal tests, such as the Teichmann crystal test and the Takayama crystal test . </P> <P> The test was named after the American agricultural chemist, Joseph Hoeing Kastle (1864--1916), who in 1901, invented and tested the crude blood test, and the German physician and chemist, Erich Meyer (1874--1927), who modified the test in 1903 . </P>

What is phenolpthalein and what was it used for in the labs
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