In the previous paper WC studied tht? leduction of ferric iron, ferricyanide and ceric salts with quadrivAznt uranium either alone or in the f)rcscncc of each other. In this pap-x we applied the reagent for the estimation of dichromatc, permanganate, tcllurate, and bromate ions scparatel~~ or in a mixture containing them tog&her with ferric and ccric salts. J~ELC~IEH, GIIJBONS ANI) Wrr;sr* studied the reduction of tlichromatc with U-i-4 and found that the rcnctiou was slug&h rrt room tcmpcraturc making the end-point rather mclistlnct, but when the titration was carried or:t :rt boo C satisfactory ant1 consistent rerulta were obtained. We pcrformctl the titratronv in the cold both in the prcscncc o[ I-ICI and I-I,SO,of various conccntrnticlns and in the prcucncc of ferric iron as :I catnIyst, 'fhc rciLction in the ~>rc?tcncc of 0.7N I-&SO, alone was rqA. ncctling only < z mlnutcs for the attainment of equilibrium at the cntl-point. I-Iowcvcr, the time incrcasccl with r&c of ;rcidity {see 'l'nhlc I) so that in 20N I-i,SO, x 0,0345rN U-t-4 (in 0.3GN I&SO& #8X. VOL. 14 (~956) URANlUM(W) IN POTENTiOMETRXC TITRATIONS. II G?5 rapid only if the acidity is Icss than 2N when it takes r~ 2 min at the end-point.The time increases to 5 and xo min when the acid concentration is raised to 4 and I+! HCI respectively. However, in presence of few drops of fcrxrc chloride the reaction velocity is increased -at the higher acidities. The decrease in the reaction rate at higher aczdities is apparently due to the rise in the Et of the II +J/ U 14 system, whtch in t 4N tl,SO, approaches the formal rcdox potential of the Cr+O/Cr-P couple (TL l.i volt). Oxzdation of Uc4 with Cr,O,+ occurs rapidly in presence of 2.5-53 I-'ICI and 3.6N f-i,SO,; the results arc quite satisfactorv. The dcfirecs of completion of the reacttons as calculntcd usine the Et value of the Cr+8/Cr-f-3 sysiem in I-jiv I-ICI or zb H,SO, as 'I, I. 1 I volt and that of the ti+s/U+h system as 0.53 and 0 G volt in both acids, amount to 5.s0"~~ and .$.3.10-l* rcspcctivcly. IXcprescntative titration cnrves arc shown in Fig. 1. C'urvc C reprcscnts the tttration of neutral dichromatc solution with U+* (m rN I-ICI). The curve cxhibtts an initmi rtsc in potential due apparently to incrcasc in the Et value of the Cr+s/Cr+3 system with rlsP: of acidity. When