3048
NOTES
efficients of 450 1. m21-l cm-I at 4900 8, 1.0 X lo41. Volume Changes on Mixing Solutions of mol-l cm-l at 1900 A, and 1.0 X lo4 1. mol-1 cm-1 at Potassium Halides and Symmetrical 1850 8 in the 0.050-0.500 torr pressure range. There was no observed effect of pressure on the average exTetraalkylammonium Halides. Evidence for tinction coefficient. Based on these figures, only 0.3% Cation-Cation Interaction. A Correction of the H I would ne$d to decompose t o give the 10% error noted in the 1900-A region. The data for HI in Table and Further Comments I are based on three indepenient measurempts above 2000 8 and two below 2000 A. The 2000-A value inby Wen-Yang Wen, Kenichi Nara, cludes all five measurements, which were in excellent Chemistry Department, Clark University, agreement in spite of the temperature and pressure Worcester, Massachusetts 01610 differences. In Table I1 our results are compared with some of the and R. H. Wood values of extinction coefficients from previous work. Chemistry Department, University of Delaware, For HBr there is satisfactory agreement with the Newark, Delaware 10711 (Received February $1, 1068) Goodeve and Taylor results down t o 2000 8, but at lower wavelengths our values are higher. Their lowest measurement was at 1890 8 and we have taken the I n the original article on this subject,’ the volume of 1850-8 value from their curve through the data. mixing, Amvex, was calculated in milliliters per mole, Romand’s results are approximately 25% lower than while the excess volume, Vex,of a pure electrolyte was ours for HBr. The discrepa!cy is slightly increased if calculated in milliliters per kilogram of solvent. The the curves are shifted 25 A to bring the observed comparison of the two volumes based on eq 5 and 6 of maxima into agreement. ref 1 is only correct if both volumes are in milliliters per Goodeve and Tayl2r made only three measurements kilogram of solvent. The correction affects only Table with H I below 2500 A and failed t o observe the maxiVI1 of ref 1 and the revised results are given in Table I. mum and minimum in the absorption curve. Our This correction does not appreciably affect the concluresults are somewhat higher than theirs above 2500 8 sions of Wen and Nara. The agreement is not as good and are l0-20% higher than Romand’s at lower wavea t low concentrations, but it is better at high concentralengths. The better agreement of Romand’s value at tions. However, with the corrected data, their arguthe minimum may be due to the effect of iodine. ment can be made even stronger. Wen and Nara conclude that cation-cation pairs are responsible for the Bayliss and Sullivan’ have reported molar extinction coefficients for I, of 2.9 X lo4,1.3 X lo5,and 1.5 X 1051. volume changes because of the agreement of the comparison of AmVex/[12y(l - y ) ] (eq 5 ) with [V“(AX) mol-’ cm-l at 2040,1960, and 1890 8,respectively, with Vex(BX)]/12(eq 6) at low concentrations and because a band width of 10 8. We have found values of
