and cerous ionL4of 1.07 X and 3.0 x 10-lo, second-order rate constants of 1.2 X lo4 and l.iX 10.' 1. mole.-' min.-', respectively, are obtained for these ions. ,Ilthough these hydroxometallic ions are considerably weaker bases than hydroxyl ion (KAfor hydroxyl ion = they are catalytically more active than the latter (for which k? = 2 x 10").!5 This would tend to lend support to the view that a push-pull mechanism is involved. Similar effects have also been observed in these laboratories with magnesium, calcium and uranyl ions. inight be expected, both calcium and magnesium, whose hydrated species have very srnall dissociation constants, shoxed this behavior c.)nly in alkaline niedia where the large hydrolytic effect of hydroxyl ions prevented quantitatiL-e measurement of the part played by the hydroxoiiietallic ions. Uranyl ion, on the other hand, cxhibited a marked effect in extremely dilute solutioii e\.en a t low pH levels. Experimental Reagents.---C .P. grade chcniicals were used as purcliaserl, without further purification. Cupric chloride vas obtained :is the dihydrate, manganous chloride as t h e tetrahydrate and ccroiis iiitrate as the hexah\-drate. GB of high purity w:is obtained from the Chernical Research Division of tlie Chernic:il \\:irfare Laboratories. Apparatus.---In earl>- experiinants the Beckman model G pH meter \\':is used. 1,nter the p H x i s hcltl constant with ;t 13cckin:tn niotlel E; automatic titrator set to deliver the srnallest pciisiblc increnients of titrant. m t l provided with a -filled iriicrol)uret gratlu:~tcd to 0.02 1111. 1Ce;ictioii teniper,tture i i i :L jacketed 2,X-iiil. beaker w:is m t i i i -
taincti a t 25.0" by it Precision Scientific Co. constant temperature circulating bath. Reaction mixtures were constatitl>-stirred with a 1-inch Teflon-covered magnetic stirring bar. .I E;lett--Surxiinerson photoelectric colorimeter provided rt-ith a So. It' filter \vas used in the atialysis for GI1. Kinetic Measurements.-Solutions of G B a r i d the InetLiI sult (on the acid side) were mixed in the reaction vessel to give the required concentration of each, antl the pH ~t-xs adjusted with base from the microburet. The amount i i f , T',, required to keep the PH constant duriiig tlic ,e of reaction (hydrolysis liberates one inclle e:ich ( i f i s i ~ p r i ~ ~ ~ y I t r i e t h ~ I p l i o s p lacid i o n i canti hydrofluoric acid) \\:is rcctircletl against time. Basic hydrolysis ant1 h c k titration of an nliquiit of tlie GB stock gave the \-olunne of basc ( 1-a i' required a t infinite time. Suitnble corrections were nplilietl to t h e d a t a to :tceount for initial acidity, \vitlidr:iw:il o f iamiples anid vvlunie changes, and tlie corrected \values [ i f ( 1" - I'L)/ I.=, which represeuts t h e fr;tetion o f GI3 remaitling, irere plotted 011 semi-l~igaritliiriic p'tper. T h e plc>ts \\sere virtuall\- linear; thus, thc reactions cshibite(l first-order kinetics. 111 three espcri~tictitstliese resiilt.~\ZC'I-C confirtried 111- direct aiial\-sis for C B b y t h e perositle~0 tolitiiiie mctllotl.'fi LImt of t h e esperiinenti Xt-ere eontlttctcd in the pH ruiigc 5-ii.S, iii irliicli the s;lx~iit:~ne~ius hydrolysis rate of GB,d u e to catalysis by !\-:iter a i i t l by h!-tlrnxyl anti hydronium ions is negligible. From tlie slopes r ~ fthc sctni-logarithinic plots, t h e first-order rate coiist:tiits, h , \vcre calculated in t h e usual manner . I i These v:irietl ivitli metal ion concentrations and PH. I n experiments \\-itti iiiangsnous a i i d cerous ions, nitrogen had ti) lie liubhletl through the reaction mixtures t o prevent oxitlation, which would h:ive changed the cimcentr;ttivxi of the dcsired metal iiin m d caused an annnialous increase in the uptake (if b:tse.
Acknowledgment.-The authors wish to acknowledge the technical assistance of Peter Hlinka, Richard Ess, Edward Costigan, Mary AI. Demck and Ra?-i~ioiidFeinlantl. 111;) 11. G e h a u l , J . ICpstein, C;, U . \ViIs l i j s z k (.h
