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proximately 20 grams per liter of Pu with a relative standard deviation of 0.05% and with an accuracy to better than 0.1%. The method has also been applied to the direct estimation of the Pu content of solutions of irradiated natural V (dissolver solution) with a relative standard deviation of 0.5% and an accuracy of at least 1.4%, using samples containing between 100 and 200 y Of Pll.
The method is remarkably free from interferences, ^cott said, since there are few reversibly titratable ions which have standard electrode potentials near that of the P u ( l V ) - P u ( I I I ) couple in an acid medium. When an ion with a standard redox potential near that of the Pu couple is known to be present, the titration can usually be carried out by the selection of a complexing medium, which increases the difference between the electrode potentials of the interfering substance and that of Pu. Several such media have been investi gated and are compared. The high acid or salt content of the medium used provides buffering action and prevents interference from varia tions in the acid content of the sample. Controlled-potential coulometry of fers an accurate and precise method for determination of neptunium, said R. W. Stromatt of Hanford. The electrolysis cell contains a Pt working electrode at which the Np(V) is titrated to Np(VI). A IN H 2 S0 4
solution is used as the titration medium. The precision of the method ranges from 1% relative standard deviation for 20-y samples to 0.05% relative standard deviation for Np samples ap proximately 1 mg. or larger. With care, as little as 2 γ of Np can be de tected and 7 γ can be titrated with a relative standard deviation of 6%. Under ordinary conditions large ex cesses of Pu, Fe, and U can be tolerated or the interference calculated. The general procedure is to first oxidize the Np to Np(VI) with Ce(IV), then electrolytically reduce the Np(VI) and excess Ce(IV) to Np(V) and Ce(III), and, finally, coulometrically oxidize the Np(V) to Np(VI). The integrated current in the last step is used to calcu late the concentration of the Np. The solutions can be analyzed for the concentrations of Np in different oxidation states with the coulometer, using a Pt electrode cell. This analysis depends upon the fact that Np(IV) is not oxidized at a significant rate during the coulometrie oxidation of the Np(V). All substances which undergo oxidation or reduction at the potentials applied interfere and must be removed or masked in order to carry out this determination. The accuracy and pre cision depend on the total Np concen tration and the concentrations of Ν ρ in the various oxidation states. An electronic controlled-potential coulometrie redox titrator for pluto-
WILD * M-20 with C a m e r a II
Fitted with Camera II, this truly versatile microscope permits continuous binocular observation of the specimen, even during exposure. The phototube deflects 2 5 % of the light to the binocular tube, with the remainder going to the Camera. Rapid, accurate focusing is achieved with a spe cial format indicating eyepiece in the binocular tube. In research and scientific exploration, the M-20 is easily capable of handling any problem which may arise in optical micro scopy. Write for interesting information about the Wild M-20 and its complete range of attach ments.
*The FIRST name in Surveying Instru ments, Photogra m metric Equipment and Microscopes.
Guest speaker at the G a t l i n b u r g Conference dinner was M . G . M e l l o n , Purdue University (2nd from right) Others present were ( left t o r i g h t ) , C . D. Susano, conference chairman, Oak Ridge National Laboratory; C . J . Rodden, New Brunswick area office ( A E C ) , characterized by the chairman as M r . Uranium; C . F. Metz, Los Alamos Scientific Laboratory, characterized by the chairman as M r . Plutonium, and M . T. Kelley, Oak Ridge National Laboratory
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