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Operation with three liquid phases was demonstrated in a staged liquid-liquid contactor. The possibility that three liquid phases could be handled in a liquid-liquid contactor normally used with two liquid phases was initially established using a laboratory batch test* The three liquid phases were obtained using a thorium flow sheet having high concentrations of both acid and thorium. To analyze the batch test, the concept of a dimensionless dispersion number for use with two liquid phases was extended so that it could be applied to three liquid phases.Based on the batch tests, continuous flow tests were run in a staged liquid-liquid contactor used for solvent extraction. A critical factor in the success of these tests was determining the position of the liquid-liquid interface in the contactor. Thus, a contactor was used which allows the position of the liquid-liquid interface to be adjusted. Actual three-phase operation was demonstrated using a 4-cm annular centrifugal contactor, albeit with a Bomewhat greater (3-4 vol. Z) aqueous-phase contamination of the organic exit stream than normal (<1 vol. %).

THE spectrophotometric determination of manganese by the distinctive colour of the permanganate ion has been used for many years. The two oxidising agents commonly employed are periodate and persu1phate.l The periodate method, first proposed in 1917 by Willard and Greathouse,2 was used in 1942 a t the Metallurgical Laboratory of the University of Chicago for the determination of manganese in uranium metal and its compounds, after prior separation of the u r a n i ~m . ~ Later in 1942, I demonstrated the feasibility of a direct determination of manganese

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Sodium perxenate, a stable salt of octavalent xenon, is used as the oxidising agent in spectrophotometric and titrimetric applications. Advantages over conventional oxidising agents are pointed out in spectrophotometric determinations of manganese, chromium and cerium. The procedures are simplified and there is a considerable saving in analysis time. The quantitative reaction of perxenate with iodide to produce iodine can be utilised in well known iodimetric procedures. Perxenate can be used in slightly alkaline solution for direct oxidation by adding an excess and back-titrating with thiosulphate. The titrimetric methods are illustrated by the determination of arsenic(II1) oxide and two hydrazinium salts.Thermogravimetric analysis results are presented for sodium perxenate dried in various ways.