Also known as fluorescent yellow, fluorescent health, fluorescent red. There are two variants: the stable red variant B and the yellow variant A. The molecular weight was 332.31. B is the crystal powder with green fluorescence. Melting point 314 ~ 316*C(decomposition). Soluble in hot alcohol, hot aniline, hot acetone, hot formic acid, slightly soluble in water, alcohol, ether, acetic acid, insoluble in petroleum ether. A is the melting point of yellow amorphous powder 314 ~ 316℃. Soluble in acetone, methanol, formic acid, slightly soluble in water, alcohol, ether, chloroform, benzene, acetic acid, xylene, nitrobenzene, insoluble in petroleum ether. It turns red when heated. Used as an indicator for chemical analysis and as a biological stain. It was prepared by the reaction of resorcinol with phthalic anhydride. Appearance: orange or light yellow red to red crystalline powder.

Smell: no smell

Melting point/freezing point (℃) : 125-127℃(dec.)

Boiling point, initial boiling point, boiling range (℃) : 620.8℃/760mmHg

Solubility: soluble in acetone, pyridine, hot ethanol, methanol, formic acid, carbonic acid and hydroxide alkali solution, and bright green fluorescence; Slightly soluble in water, alcohol, ether, benzene, chloroform, acetic acid, xylene, nitrobenzene, insoluble in petroleum ether.