Abstract
The supporting electrolyte of potassium hydroxide has been investigated from a point of application to real samples, and an analytical procedure was provided for 0.10.8 per cent of arsenic in nonferrous metals such as tin, antimony, lead, and their alloys. Then, the method was applied to lead shot and results were in good agreement with the results obtained by the photometric method. Zero point five grams of sample is taken in a beaker and mixed with 0.1 g of copper in order to avoid the volatilization loss of arsenic during the evaporation and then decomposed with 20 ml of aqua regia. The solution is evaporated to almost dryness. After adding 10 ml of hydrochloric acid, the solution is evaporated again to expel the nitric acid. The deposited salts are dissolved into 20 ml of hydrochloric acid and 10 ml of perchloric acid and transferred into a separatory funnel. Addition and dissolution of a few pieces of solid stannous chloride are continued in the separatory funnel until a yellowish-brown of the solution turns colorless. Having been added 2 ml of titanous trichloride solution prepared by dissolving 1 g of titanium metal in 100 ml of 6 N hydrochloric acid, arsenic(V) is completely reduced to arsenic(III). Arsenic is extracted twice by shaking for 2 minutes with 20 ml and then 5 ml of chloroform. The extracted arsenic is backextracted into 25 ml of water from the combined chloroform phase. After the aqueous phase is gently boiled and evaporated to expel the accompanied chloroform, it is transferred into a 25 ml volumetric flask with 5 ml of 2.5 N potassium hydroxide solution and 2.5 ml of 0.25 per cent gelatin solution and then the flask is filled to the mark with water. The polarogram should be recorded immediately after removal of dissolved air. If lead chloride is precipitated by adding stannous chloride, the precipitate must be removed by centrifugal separator and the supernant liquid can be used.
