While numerous papers have appeared dealing with the ascorbic acid content of various plant and animal tissues, and urine, only a few refer to the quantity present in the blood. Van Eekelen, Emmerie, Josephy and Wolff,l and Emmerie and Van Eekelen2 deproteinize blood, blood plasma, or serum with trichlo-racetic acid, precipitate interfering substances, chiefly SH compounds, with mercuric acetate, then treat with H2S, which not only precipitates the mercury but also reduces that portion of ascorbic acid which in blood occurs in a reversibly oxidized state. The H2S is later removed by a stream of nitrogen, and the ascorbic acid estimated by titration with 2 : 6 dichlorobenzenoneindophenol.' Gabk4 claims that loss of aslcorbic acid occurs if a solution of pure ascorbic acid is treated with H2S in the presence of mercuric acetate, and therefore, omits this step. Tauber and Kleiner5 describe a method generally applicable to plant and animal tissues (and to blood) in which the essential features of deproteinizatiori, removal of interfering substances, and H2S reduction are preserved. They estimate the ascorbic acid present either by titration or by its ability to reduce potassium f erricyanide, with subsequent development of Prussianblue upon the addition of the ferric gum ghatti reagent of Folin and Malrnros.6Our experience with several of these methods disclosed a number of difficulties. Some of the methods require considerable quantities of blood. Mercuric acetate solutions must not be over two weeks old, or filtrates containing colloidal sulphides may be obtained, particularly when the method is applied to urine. Any colloidal material in the filtrate makes it impossible to obtain a satisfactory
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