Pyrone or Phthalein Dyes

A mixture of 15 gms. of phthalic anhydride and 22 gins, of resorcinol is ground in a mortar. It is then transferred to a nickel or cast-iron vessel, and heated in an oil bath to 180°. At this temperature 7 gms. of powdered fused zinc chloride (see p. 509) are added, with stirring, during the course of 10 minutes. The temperature is raised to 210°, and maintained at this point until the liquid, which gradually thickens, becomes solid, for which 1—2 hours are required. The cold melt is removed from the vessel with a knife or chisel, powdered, and boiled 10 minutes with 200 c.cs. of water and 10 c.cs. of cone, hydrochloric acid. This treatment eauses the solution of zinc oxide and basic zinc chloride. The fluorescein is filtered off, washed with water until the filtrate no longer shows an acid reaction it is dried on a water bath. 

—Almost theoretical (32 gms.). Red powder slightly soluble in water soluble in alcohol soluble in alkali with intense green fluorescence dyes animal fibres a fast yellow. 

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