364
JOURNAL OF
CHEMICAL EDUCATION
. FEBR~ARY, 1932
IMPROVISED SPOT PLATES DEAREDITOR: In teaching qualitative analysis, I have developed the following simple idea, which may be of some interest to your readers. In determining the pH of a solution with methyl violet, or any like experiment, we have been accustomed to place drops on smooth porcelain plates, as the more expensive ones, with depressions, are not available to us. To prevent the drops from running together, a substitute for the "depression plate" may be made from old crucible covers. Every laboratory, however poor, seems to have an abundance of these. A slit is made in a two-inch cork and the knob of the cover placed in it, which provides a steady, supported porcelain dish. Sincerely yours, (MRS.)LOUISEP. MITCHELL WOMEN'SCOLLEGE UNIVERSITY OF DELAWARE NEWARK, DELAWARE
AN EQUILIBRIUM EXPERIMENT FOR AN INTRODUCTORY LABORATORY COURSE IN PHYSICAL CHEMISTRY DEAREDITOR: C. V. King's criticism [J. CHEM.EDUC.,9, 15Wl (Jan., 1932)] of our extrapolation [J. CHEM.EDUC.,8; 2065 (Oct., 1931)] of the equilibrium constant of the reaction Ag Fe+++ i Ag+ Fe++ is theoretically valid, and leads to a decidedly higher value of the equilibrium constant than the one we obtained. However, since the extrapolation of the log K, -v$ curve is carried out over such a long range it might he well to attempt to verify the result, using the available activity coefficients at the various ionic strengths used. (Here again we shall use the activity coefficients found in Lewis & Randall's "Thermodynamics," though the assumption of anything like exactness in the values for Fe++ and especially Fe+++ is certainly not warranted.) The values so obtained are given in the table.
+
"
0.0335 0.0506 0.1024
Here KO = K fA'ifFe++.
f~.+++
+
. . . . ... . . . ..
KO 0.158 0.15J 0.144
The tendency toward higher values with in-
creasing dilution indicates the probable direction of the value of the true constant and evidences the inaccuracy of the activity coefficients used. The difference between this value and the values of 0.114 obtained electrometrically by ourselves and 0.1306 obtained indirectly from an analytical
VOL.
CORRESPONDENCE
9, NO. 2
365
method by Popoff and his co-workers requires some explanation. The physical condition and purity of the silver used in the two parts is probably the greatest cause of error. In the method used by Popoff this difficulty was avoided by the use of mercury. Since the same activity coefficients were used in the electrometric determination as in the above calculation it is obvious that considerable error is introduced here. The value of KO, of the ionic strength used in the Fe++Fe+++side of the cell was 0.0567. Another possible source of error in the electrometric determination was the oxidation of ferrous iron during the time required for filling the cell and for the attainment of a constant e. m. f. We regret that it is impossible for us to investigate this reaction further. Yours truly, . E. J. SHAW MARYELIZABRTH HYDE PEOPLES
GAS LIGHTAND COKECO.
Cmc~co,I ~ I N O I S
THEODORE WILLIAM RICHARDS DR. 0.G.VILLARD, Editor
The Nation DEARDR. VILLARD: We have q u ~ t e dseveral times in the JOURNALPF CHEMICAL EDUCATION the following which, in an article on page 424 of the April 18,1928,issue of The Nation,Vol. 126, No. 3276, was attributed to the late T. W. Richards:
If I were asked to select the best chemist in any gathering, I should find out first who played the 'cello best. One of our correspondents has written us about this, and in an etfort t o find out on what occasion and under what circumstances the remark was made, we have communicated with several persons who were intimately associated with Dr. Richards. None of these has any knowledge of it, and several have intimated that it "doesn't sound like him." Can you furnish us with any information about it? Thanking you in advance for any attention you may give this request, I am Sincerely yours, NEIL E. GORDON
I am sorry to have delayed so long in sending you the information for which you asked in your letter of November llth, but the writer of the editorial in question has been out of the country and did not receive my note
