“ All four mono-hydroxyxanthones are known, and are prepared by heating salicylic acid with either resorcin, pyrocatechin or hydroquinone; they are yellow crystalline solids, which act as dyestuffs. The 1⋅7-dihydroxyxanthone, known as euxanthone, is prepared by heating euxanthic acid with hydrochloric acid or by heating hydroquinone carboxylic acid with β-resorcylic acid and acetic anhydride (S. Kostanecki, Ber., 1891, 24, p. 3983; C. Graebe, Ann., 1889, 254, p. 298) . ”

“ The carbonyl group is not ketonic in character since it yields neither an oxime nor hydrazone. When fused with caustic potash it yields phenol and salicylic acid. Mild reducing agents convert it into xanthydrol, the group >CO becoming >CH⋅OH, whilst a strong reducing agent like hydriodic acid converts it into xanthene, the group >CO becoming >CH2. ”

“ It crystallizes in needles which melt at 173-174° and boil at 349-350° C., and are volatile in steam. Its solution in concentrated sulphuric acid is of a yellow colour and shows a marked blue fluorescence. ”