Direct Titration of Sulfates Further Studies with Tetrahydroxyquinone as an Internal Indicator R. T. SHEEN
AND
H. L. KAHLER,
W.H. & L. D. Betz, Philadelphia, Pa.
50 mg. of SOa, standardized graviThe direct titration method for deterCHROEDER (1) recently metrically. An i n d i c a t o r comsuggested a direct titration mination of sulfates with the use of tetraposed of disodium tetrahydroxymethod for sulfates with the use quinone ground with dried potashydroxyquinone as an internal indicator sium chloride in a 1 to 300 ratio, of tetrahydroxyquinone as an is described. Sulfates can be determined and passing a 100-mesh screen. internal i n d i c a t o r . A direct Ethyl alcohol or alcohol denatured by this method up to 30,000 p. p. m. Phostitration method of this type by formula No. 30 or No. 3-A, or phates up to 60 p. p. m. can be eliminated offers considerable a d v a n t a g e i s o p r o p y l a l c o h o l . Phenolphthalein indicator and bromoover other rapid methods where by pH control. Isopropyl alcohol is found cresol green indicator (if phosoutside indicators, back-titrato be as satisfactory as ethyl alcohol for phates are present). Sodium chlotions, or filtrations are required. ride crystals, c. P. reducing solubility of barium sulfate and The method as d e s c r i b e d by P R O C E D U RAE. Carefully hastening the precipitation. The use of neutralize a 25-cc. sample containS'chroeder allows the direct ingup t o a proximately 2000 sodium chloride to sharpen the end point titration of sulfate in a sample p. p. m. of S& with approximately with a standard barium chloride in concentrations above 2000 p. p. m. of 0.02 N hydrochloric acid until just solution, the end point being inacid to phenolphthalein. The sulfate is described. Results obtained by temperature of the sample should dicated by the appearance of the this method check gravimetric analyses be below 35" C. and it is advisable red barium salt of tetrahydroxyto work between 20" and 25" C. within an average of 3 per cent. Compariquinone. An extensive bibliogAdd either 25 cc. of ethylalcohol son of results with the Betz-Hellige method raphy on sulfate determinations or alcohol denatured by formula No. 30 or No. 3-A or isopropyl was given in Schroeder's paper is given. alcohol. Introduce the THQ, the and further reference is not reamount to be determined from quired at this time. Table I. It is best to use a small Schroeder suggested the dispersion of the tetrahydroxyCUD to measure the mixture. Swirl the flask to dissolve the THQ: the solution will be colored'a deep yellow. Titrate with standa
