tcrniine which p1:tnchets were to be combined to form t h r various rare earth fractioi So sample of eluate escaped rorribinatioii. The itletiti of the actirvities obtained, together rvith the radiockel cal purity, \vas deterniinecl I)y c tondard decay and absorption rneasureiii~iits.
activity has been discovered among the fissioii products. T h e relative aniouiits of activity zrc such that they could reasonably ha\,? been fotrnctl either by fission or by neutron activation o f iiiicrogram amounts of Gd impurity. We are presently Results and Discussion engaged in the process of attempting to determine hfaycr and Freiling' have shown that the use of their source. 1 Jf lactic acid a t pII 3 was sufficient to give Acknowledgments.-M'c are grateful to Mr. I.. complete separation of Eu and Sin in a rcGsonable n'ish an$. 11r. R. Phillips for assistancc in the corn time. The separation of Gd from Eu, and par- duct of these runs, and to Dr. E. I < . Tonipkins and ticularly thc detection of minute amounts of TbI6' n r . N. E. Rallou for valuable sugqatioris x?id critiactivity in the presence of large amounts of lTgl cisms. activity, require even better separations. T o S U C L E A R A S D PHYSICAL CHEMISTRY B R 4 S C F I achieve these separations and still hold the time U. S. SAVAL RADIOLOGICAL DEFESSEL A I ~ . 24, CALIPORTIA required for a run down to a reasonable value, use SAS FRANCISCO was made of discontinuous gradation in eluant ~ _ _ strength. T h e best result of a number of trials is illustrated by the elution history curve in Fig. 1 . The Densities and Thermal Expansion Coefficients These separations were obtained by eluting with for Cobaltous Chloride Hexahydrate and Ethyl Iodide' 10 inl. of 0.85 'lf lactic acid, 10 ml. of 0.90 -lT, 10 ml. of 0.95 A l l ,and using 1 Af lactic acid for the BY DWIGHT A . HTXCHISOX remainder of the rim. The extrnt of decontaininaRECEIVED OCTOUER 21, 1933 tion of each rare earth from its nearest neighbors is presented in Table I. Some years back Sampson and Blcakncy2 reported the existence of a stable cobalt isotope, Cos', TABLE I to the extent of one part in 600 of Cosy. The D E C O S T A M I S A T I O N O F RAREE A R T H S FROM TTIEIR X E A R E S T later work of Mitchell, Brown and Fowler3 showed IGHBORS IN THE ELUTION P~ricrrss t h a t if Cosi exists, i t could occur to an extent no Percentage Percentage greater than one part in 30,000 of Cojg. In the years of preceding of following Planchets Rdre earth a c t i v i t y in a c t i v i t y in 1940-1946, the writer was concerned with the excombined actirity sample sample perimental determination of precise absolute4 and 11-18 ys1 n .d." relative6 densities of certain crystals, the relative 19-27 TbL61 0 15 n.d. densities being used to determine the efficiencies o f 28-34 1i.d. n.d. electrolytic separations of isotopes. T h e dual pur35-4 1 EU'= l1.d. n.d. pose, to detect the existence of Cos' and, if found, to 42-33 Sin's3 0.3 n d. determine the extent of its electrolytic separation 57-68 Pm149 n.d. 0.01 from C059, formed the basis for the prcsent experi69-92? Sd"' n.d. n.d. mental work. Although the original purposes were h .. Prla3 .. n.d. found untenable because sufficient precision in the n . d . stands for none detected. Eluate containing P r relative density of CoCla.GH20 could not be a t ri'as received in a beaker. tained without a tremendous expenditure of time, a I t is evident from the shape of the Nd peak, and large amount of the present work was already coinespecially the Sm peak, that the column was over- pleted before such conclusions could be made. Inasmuch as the experimental results obtained loaded under these conditions. The use of wider columns and proportionately higher flow rates may be of help to some workers in connection with would be expected, therefore, to give still better other problems, it was felt worthwhile to present separations in the Pm-Nd region without increasing the experimentally determined densities and esparision coefficients for CoC12.BH20 and C&I. the expenditure of time. The experimental technique of the determinatinn Treatment of duplicate samples has yielded the results shown in Table 11. These data are com- of the densities of certain solid compounds has becn parable in precision to any radiochemical analytical described previously.' The method consists of SUSresults and illustrate the possibility of using this pending crystals of the substance, the density of method t o obtain much more accurate values of which is to be determined, in a liquid of proper denrare earth fission yields than those appearing in the sity. After a density-temperature determination of the suspension liquid, the temperature a t which rrirrcnt literature. the solid crystal is suspended in the liquid forms the TABLE I1 basis for obtaining the density of the solid. C 0 M P A R I S C ) S OF RESIT1,TS F R O M DCPI.ICATE \SAMPLRS
Rare earth :irti\,ity
Pu 150 sin 157 ~,l,il:3
Xc1'47
C ( n i n t s p e r m i n u t e p e r t i , t a l sarniilr X 10 1 2
0.323 2.28 10.0(t 11.2
5
0.330 2.30
lI),(IX 1.1 -I
The source of the T b and Gd activity found in t h e w riiiis is unknown. Neithcr 7% nor Cd
(1) T h i s p a p e r is a terhnicnl r e p o r t of work < l u n e in t h e C h e m i s t r y D e p a r t m e n t a n d t h e S t a t e Engineering f:xl,erinirnt S t ~ t i i mo f t h e (:eorgia I n s t i t u t e of Tec!inoloay, A t l a n t a , C.eorgi;i ( 2 ) hl. n. S a m p s o n a n d IV. D l e i k n e y , P h y s . Re.;#, 6 0 , 7 3 2 ( I ' I X l . (9) J . J . ?ilitcheli. F1 S . R r u c n and R I ) I'owler, ihi./ , GO, (19t1) ( 4 ) H . I,. J
Determination of the Basicity of Very Weak Bases BY H . H . JAFFB RECEIVED A ~ G U S 28, T 1953
P r a t t and X a t s u d a have recently described a technique for the determination of the order of basicities of such weak bases as ketones, esters, ethers and a1cohols.l T h e basicities were expressed in terms of the rate constants ( k ) of the self-etherification of benzhydrol in the presence of p-toluenesulfonic acid and of the base under a set of rigidly defined conditions. It appears desirable to attempt to deri\re, from these rate constants, relative values of the equilibrium constants ( K B ~ +for ) the reaction B H + eB H+, where B is the base. Pratt and Draper have examined the self-etherification of benzhydrol in the presence of a small amount of p-toluenesulfonic acid, and have found the reaction to be of first order in benzhydrol.2 These authors also suggested t h a t the reaction is first order in the acid, and t h a t t.he deviations from
+
[ I ) 1: ( 2 ) I?
I: T ' r n t i n;i,i 1-: ?.latsuda, l'iiis J O U R N A L . '76, 3 7 8 O (IC4.53>. F I h t t anr! J n nr.uwr. i b i . 1 , 71, !!RAG (l!l.l!i),
Vol. 76
this order, which were observed, are due to salt effectsa The following arguments are based on the assumption t h a t the reaction is first order in both alcohol and acid. It will further be assumed t h a t all of the strong acid (H.1)) which is present in low concentration, transfers its protons to the base B or to benzhydrol (C) present in much higher concentrati~n.~ 1i-e desire to calculate the acid dissociation constant of the conjugate acid of the base (B) lis=+ = [B][ H + ] / [ B H + ]
where the quantities in brackets represent coiicc'ntrations. [H+]is given b y [H']
KCH+ [CH-]/[C]
=
where K C H + is the acid dissociation constant of the conjugate acid of C. [BH+]is given b y [BH']
-
[CH']'
[CH']
where [CH+]Ois the concentration of [ C H f ] in the absence of the base B. The rate law for the selfetherification is --d[C]/dt
=
k'[CH+][C] = k[C]
and hence [CH+]and [ B H + ] are proportional to k and (ko - k), respectively, where k" is the rate in the absence of R,the blank in the notation of Pratt and Matsuda.' Then
Since B and C are present in large concentration compared to the other quantities involved in the calculations, [B]/ [C] is constant, and equals l / a under the conditions of reference 1. Thus, Pratt and Matsuda's method combined with equation 1 permits evaluation of relative values of the acid dissociation constants of the conjugate acids of very weak bases in benzene solution. Pratt and 11atsuda' have shown tliat a correlation exists between Haminett's substituent constants )(. and the relative basicities of substituted acetophenones and ethyl benzoates, as expressed by the rate constants of the self-etherification reaction. I t is of interest to note t h a t the relativc values of I
