test indicates the sample contains hemoglobin and, therefore, is likely blood. A false positive can result from the presence of substances with catalytic activity similar to hemoglobin. This test is not destructive to the sample; it can be kept and used in further tests. This test has the same reaction with blood from any animal whose blood contains hemoglobin, including almost all vertebrates; further testing would be required to determine whether it originated from a human. Synthesis Phenolphthalein can be synthesized by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions. It was discovered in 1871 by Adolf von Baeyer. The reaction can also be catalyzed by a mixture of zinc chloride and thionyl chloride. See also Bromothymol blue Litmus Methyl orange pH indicator Universal indicator References External links Page on different titration indicators, including phenolphthalein PH indicators Triarylmethane dyes Phenols IARC Group 2B carcinogens Phthalides Laxatives