alizarin

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An orange-red crystalline compound, C₁₄H₆O₂(OH)₂, used in making dyes.

Century Dictionary and Cyclopedia

1. n. A peculiar red coloring matter (C₁₄H₈O₄) formerly obtained from madder, and extensively used as a dyestuff. It was discovered in 1824 by Robiquet and Colin, who obtained it by digesting madder-root with alcohol and treating this with sulphuric acid, thus producing a black mass which they called charbon de garance. On heating, this yielded a sublimate of alizarin in long, brilliant, red, needle-shaped crystals. It is now artificially prepared on a large scale from anthracene (C₁₄H₁₀), a product of the distillation of coal-tar. It forms yellowish-red crystals insoluble in water, difficultly soluble in alcohol, but readily soluble in alkalis, giving to the solution a purplish-red color and beautiful fluorescence. It has acid properties and unites with bases.
2. n. Commercial alizarin is sold in the form of a yellow paste containing 20 per cent. of dry substance, and, less frequently, as a dry powder. The dry substance in the paste is seldom pure alizarin, but contains varying amounts of flavopurpurin and anthrapurpurin, both of which have properties similar to alizarin. Natural alizarin derived from madder contains purpurin in addition to the above. The nature of the various commercial alizarins is often designated by suffixed letters or numbers. Thus alizarin I, alizarin P, and alizarin V are nearly pure alizarin and give blnish reds, while alizarin CA, alizarin G, etc., contain anthrapurpurin or flavopurpurin, or both, and give yellowish reds.

Wiktionary

1. n. a type of red or crimson dye

GNU Webster's 1913

1. n. A coloring principle, C14H6O2(OH)2, found in madder, and now produced artificially as an an orange-red crystalline compound from anthracene. It is used in making red pigments (such as the Turkish reds), and in dyeing.

WordNet 3.0

1. n. an orange-red crystalline compound used in making red pigments and in dyeing