In Japanese Agricultural Standard for sawn wood, a spectrophotometric method with curcumin is adopeted for the quantitative determination of boric acid content in wood treated by boron insecticides. The present work deals with another, more rapid analytical method for the determination of boric acid by means of spectrophotometry with carminic acid. A specimen is subject to wet decomposition by sulfuric acid-phosphoric acid-hydrogen peroxide in a round-bottomed flask fitted with a Kjeldahl connecting bulb. Boric acid in the decomposed mixture is allowed to react with carminic acid in concentrated sulfuric acid, and the absorbance of the resulting solution is measured at 600 nm. This method presents no difficulty in the decomposing procedure, good color development, and satisfactory rapidity in whole analytical procedure.

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