Azulin

Red coralline [52] or Peonine is obtained by heating crude aurin with ammonia under pressure, and] is probably intermediate in composition between aurin and pararosaniline. Azulin is obtained by action of aniline on aurin, and is probably an aurin containing aniline groups [53]. This blue dyestuff was largely used before the introduction of aniline blue. 

It may be distilled without decomposition. It absorbs HjO from damp air to form a hydrate, which crystallizes in six-sided prisms, fusible at 16° (60°.8 P.). Its vapor is reduced to benzene when heated with Zn. It combines with HjSOi to form phenyl-sulfuric acids. It forms trinitrophenic acid (q.v.) with HJfOj of 36° B. When heated with HsSO and oxalic acid it forms rosolio acid or coraUin, which is a mixture from which the pigments aurin, peonin, azulin, and phenicin are obtained. 

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