Abstract
This method is a turbidimetric determination of barium sulfate by estimating the light absorbancy of barium sulfate suspension. The sample is dissolved in nitric acid-hydrochloric acid mixture for conversion of the sulfur to sulfate, and the selenium is separated by volatilizing it off as a bromide by addition of hydrogen bromide. The process is carried out in the presence of a certain amount of sodium nitrate in order to avoid the loss of sulfate.
For determination of turbidity, an aqueous solution slightly acidified with nitric acid containing 65% of an equal mixture of ethanol and propylene glycol is used. A 0.25M barium chloride solution is also prepared by using the same solvent. Under these conditions the relationship between the amount of sulfate and the light absorbancy was the most satisfactory, as indicated in Fig. 2. The effect of concentration of acid, the method of mixing, and the effect of coexisting substances were investigated in detail; and a method of determination up to a limit of 0.0005% sulfur in selenium with ±4% error was established. The time required for this procedure is 8 hours. The merit of this turbidimetric method is that the determination of a micro quantity of barium sulfate, which was difficult by heretofore known methods, can now be accomplished with good accuracy. The results of application of this method to the nephelometric method are also described.
