T o /,he Editor: I have been very favorably impressed with the series "Safety in the Chemical Laboratory," which is serving a very important function in bringing safety information to the attention of your readers. I have hoped to see the mention of one simple safety precaution rrbich does not seem to be used commonly. This is the practice of noting the date of receipt on t,he label of a rontainer of chemicals. Not only does t,his serve as a useful met.hod of determining the age of chemicals, surh as ethers, which can become hazardous on standing, but it also avoids wasted effortsin working with chemicals which are apt to decompose on prnlonged standing.
A more accurate statement would substitute "inconsistencies" for 'Lerrors" since t,he connection wit,h experimental error is indirect. The discrepancies more likely arise from inconsistencies between t,he selected values of ACAO,AGro, or 6' given by Sanderson and those used by Professor Noyes in the derivation of AGno. It should be emphasized that the hydration energy AGRo is not observed experiment,all.v hut is in effect calculated from selected values for Go by an inverse of Sanderson's process for ralrulating &.' Exact agreement should be obtained with the use of a single self-consistent set of select,ed values for AGAo, ACrO and 8'. This is the raison d'&treof the ". . . seemingly accurate free energies of hydrat,ion . . ." Self-consistency may be easily lost hy combination of values from rkfferent sources, whet,her these are experiments subject to error or, as in this case, different critical compilations of select,ed values such as those of NBS and Latimer. Inconsistencies between compilations arise because of the use of different criteria or different sets of experimental data in the ~elect~ion process. Both factors relat,e to experimental error but the connection is not simple. T o the Editor: The preceding comments do not detract from ProI n my paper, "Stepwise Formation Constants of fessor Sanderson's conclusions or from the remainder Complex Ions, A Student Experiment" [THIS JOURNAL of his discussion. 44, 46 (1967)1, I did an injustice to Professor David E. Goldberg of Brooklyn College by not mentioning his more detailed paper on the same topic, [THISJOURNAL, 39,328 (1962) 1. My aim was to present as simply as possible an example for teachers who have not realized how easily this tapir might be presented to undergraduates. I might mention that the heavy ammonium ion buffering (2 M N H 4 S 0 3 used in Bjerrum's work keeps the pH low and reduces occurrence of "variable result,sV reported by Goldberg and ascribed to OH- complexing. T o the Editor: While this may not be the best research technique, I feel it is desirable in the number of variables for the In an article entitled, "An Experiment in Activated student to contend with in a first meeting with such a Aromatic Nucleophilir Substitution" [L. TC. DYALL, system. mrs JOURNAL, 43, 663 (1966)l the author states that the potential energy diagram for formation of the B. GUENTHER WILLIAM R'leisenheimer intermediate formed from methyl picryl ether and sodium methoxide has been described by Fendler [a. H. FENDLER,Chem. & Indus. 764, (1965)). A more appropriate reference to potential energy diagrams for Meisenheimer intermediates, and one in keeping with the aim of Dyall's article, is that of .I. >filler [J. Am Chem. Soc., 85, 1628 (1963), and earlier refT o the Editor: erences included]. lliller's extensive and pioneering work on the energetics of intermediate complex formaThe discussion "On the Significance of Electrode tion not only provides much insight to the nature of Potentials" [J. CHEM.EDUC.,43, 584 (1966)l by Prothese energy diagrams hut also deserves to he recomfessor Sandersou is pertinent and informative. Further mended as a profitable model for student study. comment is desirable, however, on the comparison between calculated and experimental electrode potentials and the resulting statement that, "Discrepancies call attention to errors either in experimental measurements of the potentials or in at least one of the component free energies."
Volume 44, Number 7, July 1967
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