STANDARD BARIUM SULPHATE SUSPENSIONS.

It has been shown that the state of the volumetric flask, the order of mixing the reagents, and the temperature of the reaction are important influences on the optical density readings of standard barium sulphate suspensions. The rate of mixing the reagents does not appear to be important.A reproducible method for preparing a standard barium sulphate suspension with an optical density equivalent to 100 mg. protein per 100 ml. is described.