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suggested a direct titration method for sulfates with the use of tetrahydroxyquinone as an ized to the acid side of the phenolphthalein end point. Phosphate was found to be an interfering ion.It was the aim of this investigation to extend the sulfate range, which was found possible, and to find a diluent that could be used in place of ethyl or denatured alcohol, because of the difficulty of obtaining either the ethyl or the denatured alcohol in many plants, owing to certain government restrictions. Isopropyl alcohol was found to answer this purpose. Elimination of the phosphate ion is desirable and it was found that this ion could be eliminated up to 60 p. p. m. by changing the pH value of the titrating solution to about 4.0. ExperimentalThe indicator used throughout this study was manufactured in the Betz laboratory and considerable quantities of this material have been supplied to the field.Detailed directions are given below for a determination of sulfate by direct titration using THQ as the indicator.Materials and Reagents. Standard barium chloride solution, the strength varying from 1 cc. = 1 mg. of SOi to 1 cc. = 50 mg. of SOi, standardized gravimetrically. An indicator composed of disodium tetrahydroxyquinone ground with dried potassium chloride in a 1 to 300 ratio, and passing a 100-mesh screen.Ethyl alcohol or alcohol denatured by formula No. 30 or No. 3-A, or isopropyl alcohol. Phenolphthalein indicator and bromocresol green indicator (if phosphates are present). Sodium chloride crystals, c. p.

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The determination of sulfur in rubber by the precipitation of oxidized sulfur as sulfate by means of barium chloride and the back-titration of the excess barium has been shown to be as accurate as the gravimetric procedure in solutions of the characteristics described above, for the determination of sulfur, with the use of tetrahydroxyquinone as the indicator. The method is very rapid compared to the gravimetric procedure and after oxidation to the sulfate form in solution, a determination can be made on a single sample in 20 to 30 minutes; with groups of analyses this time can be greatly reduced when compared to the time required for a single analysis.

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