above what seemed to be the true : Pk curve.The solutions, at the midpoint of reduction, were dark brown in color, that is, deeper in color than the quinone solution itself. While no satisfactory account of these peculiarities suggests itself, it is of interest that Sullivan, Cohen and Clark16 encountered entirely analogous discrepancies in this same region of alkalinity in their investigation of the electrode potentials of indigo sulfonates. While these authors considered the effect specific to borate buffers, though indeed certain divergences with alkaline phosphate buffers were recorded, no differentiation between borate and phosphate buffers was apparent in the present case.It seems likely that some phenomenon not yet understood is in operation at the particular alkalinity at which few but borate buffers are available.Thus glycine buffers are out of the question because the sulfonated quiñones react with glycine.Only those results about which there is no cause for uncertainty have been included in the table. Fortunately, these results furnish the comparison desired.In conclusion I wish to express my gratitude to Professor William Henry Perkin, Jr., for his many kindnesses during a portion of this work. Summary Sodium 6,7-indazole-4-sulfonate has been prepared and characterized and compared with potassium /3-naphthoquinone-4-sulfonate. The normal reduction potentials of the two substances at 25°are 0.620 v. and 0.630 v., respectively, which indicates a close relationship between the pyrazole and the benzene systems.
In carrying out the test the ammoniacal filtrate is taken from the bismuth separation, the excess of ammonia is removed either by boiling or by careful neutralization with acid. If sufficient ammonium salts have not been added in the course of the analysis, 3 or 4 cc. of a 10% solution of ammonium chloride is added at this time. The solution is then treated with an equal volume of saturated sodium bicarbonate solution. The presence of cadmium is indicated by a turbid, white precipitate which is easily noted in contrast to the clear blue of the copper solution.The test is sensitive to about 0.1 mg. per cc., which can be detected without difficulty in the presence of five times that amount of copper.Failure to remove mercury or lead before the bismuth separation does not interfere with the test.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.