CORRECTIONS
Rapid Argentimetric Determination ,of Halides by Direct Potentiometric Titration-Addendum the appearance of the original article on this subject S [Shiner, V. J., Jr., and Smith, M. L., ANAL.CHEar. 28, 1043 (1956)] several errors have been called t’o the attention of the ISCE
authors. Riemann (W. Riemann 111, private communication) has pointed out that t’he values in column 3 of Table I should be aesociat,edwith the mid-points of the interval of columns one and t,wo, instead of wit.h the ends, as was done. This produces an error of 0.02, 0.04, and 0.02 ml., respectively, in t,he end point values det,ermined for chloride, bromide, and iodide and would produce a constant error of +0.0004, $0.0008, and $0.0004 meq., respectively, for chloride, bromide, and iodide in subsequent titrations. The fact that the data in Table V came out so well may be due to compensatory systematic errors of the same order of magnitude, or it may indicate that there is a slight error in the Table I titrations and that the end point values taken were verjnearly correct. In any analysis one should determine a titration blank by a series of standard determinations; if this is done in this case, the value taken for the end point e.m.f. is not critical, provided it is on the steep part’ of the e.m.f. curve. If it is determined that there is a small blank, it can be eliminated by a change in the e.m.f. used for the end point. Because of the correction noted above, the end point e.ni.f. values given in column 4 of Table I1 should be 254, 174, and 55 instead of 257, 197, and 114. Riemann also points out that K s , p .value given for silver iodide is a typographical error and should be 1.5 X lo-’$. Table I also contains some typographical and arithmetic errors: 207.08 in column 2 should read 223.28: in column 3 the corrections in order are, 2.00 to 0.70, 9.87 t o 8.87, 62.56 to 63.10, 8.13 to 8.10, 11.55 to 11.58, 74.70 to 149.40, and 72.00 to 144.00. Przybyloq-icz (E. P. Przybylowicz, private communication) has called to the authors’ attention the fact that, as written, the paper indicates that the end points used in the t’itration of the mixed halides were the same as those obtained in the titration of the separat,e halides. This is incorrect; the end point e.m.f.’s for the mixed halide titrations should be determined as the equilibrium e.m.f.’s exhibited by the cell when enough standard silver nit,rate has been added to a standard mixed halide solution to precipitate in turn all of the iodide, bromide, and chloride. A plot of e.m.f. us. standard silver nitrate added, for such a titration, should give breaks n-hich include the equivalence points for each halide. However, the mid-points of these breaks will not necessarily coincide exactly with the calculated end points. The end point e.m.f.’s chosen should, of course, be the ones which give the correct titer. We have found these end points to be reproducible over periods of 4 or 5 days. Przybylowicz has also pointed out that for widely different ratios of chloride, bromide, and iodide these end points Rill not be exactly the same, so that standardization should be done with a standard sample approximating the composition of the unknown. In checking our procedure Przybylom-icz reports t,hat he consistently obtained the break in the e.m.f. curve at the bromide end point 10 to 14% high and at the chloride end point low by the same amount in terms of silver nitrate titer. In the authors’ experience the high results at the bromide equivalence point have
been associated n-ith a nonequillbrium condition in the cell brought on by coagulation of the precipitate. This can be avoided by using additional detergent (as much as 5 ml.), stirring vigorously, and allowing a little time for the cell to come to equilibrium near the end point. Kith enough detergent present, this time need be only about 1 or 2 minutes. We have not been able t o obtain satisfactory reproducible e.m.f. curves without using the detergent, because of excessive potential drift, and therefore believe the detergent to be necessary for satisfactory results. Przybylowicz reports that he has not been able to obtain the bromide break very near the bromide end point in the presence of the detergent. even using the additional precautions mentioned above. He also reports that he is able to obtain satisfactory e.m.f. cuives without detergent in solutions of high ionic strength (0.6.11 sodium acetate-0.6hf acetic acid), and therefore claims that the detergent is not useful in the mixed halide determination. TT’e believe that it is significant that prior to our work, none of the published procedures for potentiometric halide determination involved titrations to fixed end points. We also did not find this practical for separate or mixed halide determinations, except in the presence of the detergent. Both sets of experimenters agree that the potentiometric method is useful for mixed halide determination in the concentration ranges around 0.00131, although there is disagreement as to the usefulness of the detergent.
V. J. SHIXER, JR. MORRISL. SMITH Indiana University Bloomington, I n d .
Components of Gas Phase of Cigarette Smoke In the article on “Some Components of Gas Phase of Cigarette Smoke’’ [Osborne, J. S., Adaniek, Stephen, and Hobbs, ?vl. E., ANAL CHEX 28, 211 (1956)l the values for COS given in Table VI under the heading “Volume, Cc./Puff a t NPT” should be reduced by a factor of 10. The correct values are: 0.24, 0.08, 0.51,and 0.11 X ~ I A R CE. US HOBBS
2028
X-Ray Powder Diffraction Patterns of Benzoic Acids In Tables I and I1 of the art.icle on “X-Ray Powder Diffraction Patterns of Benzoic Acids” [Rose and Van Camp, ANAL. CHEY. 28, 1430 (1956)l the data for y-resorcylic acid and 8resorcylic acid were interchanged.
