I. The Iodometric Determination of Zinc. II. Investigations in the Chemistry of Rhenium

Part I describes a study of the iodometric determination of zinc. The equilibrium of the ferricyanide-ferrocyanide and iod1de-iodine couples is shifted far to the right by zinc ion, which precipitates ferrocyanide and hence causes iodine liberation. Conditions based on this principle were developed for a rapid, accurate titration of zinc. The results of a series of investigations of the reactions of oxidation states of rhenium in aqueous solution are presented in Part II. These reactions were studied by spectrophotometric and analytical experiments for the states ReVII, ReV, ReIV, ReI, and R-I. ReV was formed rapidly in a light green solution by addition of 1 or 2 equivalents of stannous chloride to solutions of perrhenic acid, HReO4 , in 4 F hydrochloric acid; this oxidation state has been previously reported, Similarly, yellow-brown ReIV was verified as the product with further addition of stannous chloride. Brown ReIV prepared from hydrochloric acid with rhenium dioxide had reactivity similar to the stannous chloride preparations, but yellow-green ReIV Cl=6 was very resistant against a wide variety of oxidizing agents. It was confirmed that Re-I was formed by treatment of dilute solutions of perrhenic acid, in hydrochloric acid, by amalgamated zinc. Oxidation of Re-I by HReO4 or O2 formed first brown Re+I and then yellow Re . Titration of Re-I with CuII gave Re+I and copper metal.