NOTES AND CORRESPONDENCE Materials Used in Chemical Engineering Operations SIR: Referring to the article by Roetheli and Forrest [IND. ENQ.CHEM.,24,101s (1932)], we should like to congratulate the authors on the excellent layout of the material and the large amount of information given. We note, however, that under the heading of hydrofluoric acid they state that the “only material totally resistant and in use is wax,” and no mention is made of the use of gutta-percha for this purpose. This material is exceptionally resistant t o this acid and has been used and is still used in the form of bottles, jugs, and carboys, and for tank linings for conveying and holding this acid. It may not be generally known that gutta-percha of suitable quality resists strong hydrochloric acid as well as strong hydrofluoric acid and is very resistant to nitric and sulfuric acids (of a strength less than 50 per cent by volume. I t also resists strong alkaline solutions. Mention might also be made of the use of gutta-percha for packing purposes in the form of joint rings of round section, of the flat washer type, and of pump and ram rings. In cold systems these articles are considerably used in this country. TELEGRAPH CONSTRUCTION & M.4INTENANCE COMPASY,LTD. LONDON, S. E 10 ENGLAND I
UXIYERBITP O F Kaxs%s LITVRENCE, Kasu. .July 2 8 , I932
SIR: Davidson is correct in his statement that :I plot of z against log, P could hardly yield satisfactory values for this integral (Equation 7 as given in the original article) by graphical integration. If the following discussion were substituted for that part of the original publication between Equations 6 and 7 on page 516, the difficulty would be eliminated and the results shown to he correct:
Rewritten,
Since the fugacity approaches the pressure as pressure approaches zero, and equals the pressure a t zero pressure,
September 28, 1932
.
d u e s for this integral by graphical integration, since the area under the curve, from a pressure of zero to any desired value of t,he pressure, mould always be infinite. It is not clear, therefore, how the values offp, plotted in Figure 1, were obtained. ARTHURJT, DAVIDSOX
.
I n f o = In Po
SIR: Regarding the communication from the Telegraph Construction and Maintenance Company, r e thank theni very much for their interest and criticism. In a compilation of this type, information on some of the better-known materials is readily available to the compiler, whereas some important facts regarding materials such as guttapercha, whose limitations are less generally recognized, do not reach him and are consequently omitted, not because of any particular prejudice on his part but because the facts :ire not part of his knowledge. We appreciate very much receiving informational criticism of the kind in this letter, inasmuch as it tends to complete the information which we have endeavored t o present, and to make available more tools for the solution of the ever important materials problems. B. E. ROETHELI ~ A S S A C H U S E T T SINSTITUTE O F
TECHHOLOQY
CAMBRIDGE, MASS. October 13, 1932
Fugacities of Paraffin Hydrocarbons SIR: There appears to be a rather serious error in Equation 7 of the article on “Fugacities of Paraffin Hydrocarbons,” by Selheimer, Souders, Smith, and Brown [IsD. ENG.CHEM.,24, 515-17 (1932)]. In the sentence immediately preceding this equation, the authors say: (‘Since the fugacity is equal to the pressure when the pressure is zero, the lower limit of the left-hand side of Equation 6 may be omitted.” This statement is erroneous, since the value of In f, when f is zero, is infinitely negative, and therefore obviously not negligible. As a result of this error, In f~ is placed equal (Equation 7 ) to a definite integral whose value is evidently infinite, since In P is - when P is zero. A plot of z against In P could hardly yield satisfactory 8-
(7)
G. G. BROWS UNVERSITYOF MICHIG 1s AXK .ARBOR* MICH. October 1 2 , 1932
Esterification Processes and Equipment SIR: 0. B. Helfrich, vice president of the Kessler Chemical Corporation, has called to my attention certain statements made in my articleon esterification, IND.ENQ.CHEM.,24, 1096 (1932) ’ The assertion that the ternary mixture of ethyl acetate, ethyl alcohol, and water could be sold as such is not correct a t present because such a mixture, owing to the high percentage of water, is not feasible for any manufacturing operation of which we know. The statement was also made that it is advisable to use acetic acid more dilute than glacial in the manufacture of a butyl acetate of high ester content. Helfrich’s experience has been that the concentration of acetic acid used is best governed by the relative costs; a t the same rost. glacial acetic acid is more economical to use. D. B. KEYEE UNIVERSITY O F ILLISOIJ URBANA, ILL. November 4. 1932
In the article “Surface Tension of Tooth Paste CORRECTION. Solutions’’ by S. M. Gordon and E. W. Shand [IND. ENQ.CHEM., 24, 1148-52 (1932)], “Surface tension in dynes per sq. cm.” under Figures 1 and 2, on pages 1149 and 1151, and in Table I, on pages 1150 and 1151, should read “Dynes per cm.”
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