Cobalt is considered to be the chief component in the tungsten carbide mixture responsible for hard-metal disease. An animal inhalation study was undertaken simulating conditions under which these workers in the tungsten carbide industry are exposed to cobalt. In this semichronic study, miniature swine were exposed to an inhalation of pure cobalt metal powder at concentrations of 0.1% mg/m3 (present TLV) and 1.0 m/m3. At peroidic intervals, the following studies were performed: pulmonary function tests, electrocardiograms, x-ray examinations, blood and urine tests, electron microscopy, and light microscopic pathology. Early detection of pulmonary disease is apparent from the pulmonary function tests showing a mark decrease in lung compliance, and from electron microscopy showing an increase in the amount of septal collagen. This study demonstrates that the present TLV of 0.1 mg/3 for cobalt seems to be too high, even at this relatively brief duration of exposure.

Though persulfate in acid1 or neutral solutions2 has frequently been applied as a qualitative reagent, its use in alkaline3 solution has been limited to the precipitation of cobaltic oxide. Using potassium persulfate in potassium hydroxide solution, instead of ammonium persulfate in sodium hydroxide solution as used by Pozzi-Escot, a more complete precipitation of Co203 can be made (1:1,000,000).Comparable precipitations of black Ni203 can be made from nickelous solutions by treatment with alkaline persulfate. In the absence of cobalt, it is a characteristic test for nickel, since its black will cover up the colors of other metallic hydroxides. Also in the presence of metals whose hydroxides are soluble in fixed alkalies, it can give a separation of either nickel or cobalt or both of these metals. Conversely nickel or cobalt is a qualitative test for persulfate.Cyanides.-Alkaline persulfate oxidized cyanides, ferricyanides, ferrocyanides, nitroprussides and thioazanates to cyanic acid, as indicated by the following test. To any one of these, add the reagent and heat to boiling. Acidify with hydrochloric acid and again make alkaline. Moist red litmus paper on the convex side of a watch glass covering the beaker turns blue, owing to the liberation of ammonia. Without persulfate, the litmus paper remains unaffected.Thiosulfate, but not sulfite, or arsenite, is oxidized by the reagent. .Sodium peroxide liberates oxygen. These and other reactions will be studied.

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