spopsisPolyethylenimine (PEI) forms a copper chelate with a N/Cu ratio of about 5 and with extinction coefficients of about 175 at 63$0 A. and 4250 a t 2694 A. Solutions of PEI-copper chelate obey Lambert's and Beer's Iaws and show increased optical density in the presence of chloride ion. Above pH 4.25, hydrogen ion has little effect. A comparison with the copper chelate of polyvmylamine suggests that PEI has a highly, branched structure. Analysis of PEI via its copper chelate is described. 1993 1994 V r .

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Sedimentation and diffusion constants were determined for electrophoretically purified Vi antigen before and after mild alkaline hydrolysis. The molecular weight of the intact antigen was found to be 1.7 X 106. Mild alkaline hydrolysis completely removed 0-acetyl, reduced the molecular weight to 1.0 x 105, and lowered the intrinsic viscosity from 8.0 deciliters/g to approximately 0.5 deciliter/g. Infrared spectra of the two antigen preparations were also compared.