June, lOGC1
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COJIPONEKTS IN SOLUTIONS C o . v ~ a rISG i CHARGED ~IACHOMOLECI-LA~L SPECIE^ I03
any cesium analog would be expected to be more dissociated, such a ratio is not likely to reappear heterogeneously. The 4: 11 ratio which exhibits a large liquidus field is expected to reoccur while the 1:2 value may or may not reoccur since its field is small, w e n though the liquidus slope does not indicate a high degree of dissociation in the liquid state. The 2 :3 ratio is most certainly expected to appear, n i t h greater submergence of the field, however. The 1: 1 ratio also exhibiting a slightly submerged field is expected to repeat in a similar manner, hut the 4 : 3 compound whose liquidus field is pr zctically suppressed should not reoccur.
From examination of Fig. 1 it is apparent that the 4 : 1 ratio should repeat. I n order t o further expand on these considerations concerning compound retention, studies of the systems Csz0-Nb20e and M2120-V206have been initiated and will be discussed a t some later date. Acknowledgment.-The authors wiih to thank Miss B. Agule for performing the density measurements, l l r s . J. Alineo for assisting with the therniul evaluations, Mrs. C. Pfister for taking the ponder photographs, Philips 13lectronics for making fluorevence analysis equipment available aiid Miss 11. Berry of this Laboratory for performing the fluoresceiicc analysis.
OK' THE DEFIXITIOK' OF COMPOSEST8 IS SOLUTIOKS CONTAISISG CHARGED RZACRORiIOLECULAR SPECIES' BY EDWARD F. CASASSAAND HENRYK EISENBERG Mellon Institute, Pittsburgh, Pennsylvania Received November 90,1968
The choice of electrically neutral components in a three-component solution containing a macromolecular ionic species anti
a diffusible salt (e.g., protein, sodium chloride, water) is discussed. The definition obtained b p equating inner and outer salt concentrations in a dialysis psperiment is shown to offer considerable advantage in the interpretation of data from light scattering and equdibrium ultracentrifugation.
I n any study of the equilibrium properties of multicomponent solutions containing charged macromolecules and small ions, the problem of a suit'able definition of independent components must be considered. Since it has not always been recognized that, the well known relations developed for two-component systems cannot be applied arbitrarily to multicomponent systems, interpretations of experimental data have sometimes been subject to error or ambiguity, particularly in connection ki-ith the definition of components. One calls t o mind, for example, discussions of hydration in the earlier lit8erat8ureon the ultracentrifugation of proteins. Although misconceptions still appear occasionally, analyses of osmotic pressure, light based scattering 3-7 and equilibrium on rigorocs thermodynamic and statistical mechanical rea'soning, nom provide an adequate basis for design and interpret'ation of experimental studies. Since all that is required thermodynamically of :,n independent component is t'hat it be electrically neutral, one is obviously left with a wide range of correct definitions, some of which may, however, be more useful or convenient than ot,hers iii particular circumstances. It is the purpose of this note to point out the consequences, in the thermodynamic treatment of light scattering and sedinientat,ioii equilibrium, of a particularly (1) This w o r k was supported in p a r t by a grant (NSF-G7COR) of t h e National Srience Foundation. (2) G. Scatchard, J . Am. Chem. Soc., 6 8 , 2315 (1946). (3) H. C. Brinkman and J. J. Hermans, J . Chsm. Phus., 11, 574 (1949). ( % ) W. 11. 3t
