Radioactive Isotope Dilution Procedures. Utilization of the Radioactive Isotope Dilution Procedures for Special Types of Chemical Problems. Quantitative Determination of the Three Individual Components of Mixtures of Dibenzyl Sulfide, Sulfoxide and Sulfone as an Illustrative Example

Abstract

INDUSTRIALAND ENGINEERING CHEMISTRY standing 2 days, but it is probably advisable to make up only sufficient for the day's requirements. Sodium Acetate. With local ores the essential minimum was 5 ml. of sodium acetate solution. The quantity of sodium acetate necessary would vary with different products and it was decided that a safe addition was 10 ml.Nitric Acid. It is essential to add sufficient nitric acid to dissolve any precipitate formed with sodium acetate and to destroy color complexes formed with metals other than cobalt. It was found that the nitric acid could be increased to 15 ml. without affecting the color development, when 10 ml. of sodium acetate were used. The presence of certain elements necessitated alterations in procedure. Very high iron, manganese, etc., required more than the standard addition of 5 ml. of nitric acid to clear the precipitate formed with sodium acetate.Time of Boiling. The final boiling had to be carefully controlled. The solution must be brought to a vigorous boil, nitric acid added, and the boiling continued for from 1 to 2 minutes. The extension of the boiling time to 3 minutes caused little change, but any further extension resulted in a definite bleaching of the cobalt color. On the other hand, any decrease in boiling time prevented the full development of the red color. This confirms the work of previous investigators {1).Fading of Color on Exposure to Light. Samples permitted to stand for 24 hours in Erlenmever flasks fitted with loose covers were practically unchanged. On standing for a farther 24 hours there w'as an observable lessening of color. The flasks were exposed to diffused sunlight for half, of this period. The effect of exposure to light, although slight, is apparently more pronounced than experienced by Hayw'ood and Wood. This is probably due to the more intense sunlight prevailing in Africa.It would appear that w'hen dealing w'ith quantities of cobalt between 0.01 and 0.50 mg. the control of conditions need not be so critical as described by Kidson and Askew {2), who were w'orking with quantities of cobalt as low as 0.0001 mg. While Haywood and Wood (1) report good results with very high cobalt-containing steels, the authors have found the greatest range of usefulness Vol. 18, No. 8 of this method to lie in the lower concentrations of cobalt in mining and metallurgical products. SUMMARY A modification of the nitroso R salt method for cobalt is described which should have xvide adaptability for the determination of small quantities of this element in metallurgical products and similar materials. Results compare very favorably in accuracy and precision with those obtained by the longer standard gravimetric procedures, and the recovery of added cobalt is complete.