DEFINITION OF SURFACE TENSION
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(4) CHOPPIN, FREDIANA, AND KIRBY: J. Am. Chem. SOC.61,3176 (1939). (6) COFFIN:Can. J. Research 6,036 (1931). DICEYAND COFFIN:Can. J. Research 16, 280 (1937). (6) COMPERE: Proc. Louisiana Acad. Sci. 6, 93 (1942). (7) EMICHAND SCHNIIDER: Micro-Chemical Laboratory Manual, p. 121. John Wiley and Sons, Inc., New York (1932). AND EYRINQ: The Theory of Rate Processes. McGraw-Hill Book (8) GLASSTONE, LAIDLER, Company, Inc., New York (1941). (9) HINSHELWOOD, HARTLEY, AND TOPLEY: Proc. Roy. sor. (London) A100, 575 (1922). (10) HURDAND BLUNCK: J. Am. Chem. SOC.60,2419 (1938). J. Am. Chem. SOC.61,3367 (1929). (11) HURDAND SPENCE: AND EVERSOLE: J. Am. Chem. SOC.61,3203 (1939). (12) MAKENS (13) NELSONA N D ENDELDER: J. Phys. Chem. SO, 470 (1926). (14) STEACIE: Proc. Roy. SOC.(London) Al27, 314 (1930). (15) THOMPSON AND FREWING: J. Chem. SOC.1936, 1444. Rev. Sci. Instruments 6,28 (1934). (16) ZABELAND HANCOX:
COMMUNICATION TO THE EDITOR THE DEFINITION OF SURFACE TENSION' According to the classical definition, surface tension is a force per unit length, tangential to the surface and is expressed in dynes per centimeter. It can also be defined as a work per unit area, in which case its dimensions are dynes cm.
c~ = erg cm. cm.2
Both expressions are obviously identical. Thus it is quite legitimate to use either of these definitions and express surface tension in terms either of dynes per centimeter or ergs per square centimeter. In the literature, however, substantial departures from the above definitions are unfortunately very frequent. For example, in French literature, it happens very often that the surface tension is stated as a tangential force per unit area. Although it has been pointed out that it is wrong, this practice is still in force. The author had an amusing experience in this matter. Having sent a paper to a French journal some years ago, he received the proofs with dimensions changed to dynes/cm2. throughout the paper. Having corrected it, the author received the second proofs in which the squares were reinstated. The editorial staff yielded, but only after a lengthy dispute. Similar difficulty has been experienced in this country by the author. In lecturing on these subjects for a number of years, the author has always given his students the classical definitions as above, but he has noticed that the students have great difficulty in assimilating them. In support of their attitude, some of them brought a number of books in which the definition was at variance with the 'Received March 1,1943.
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NEW BOOKS
classical one. Some of these definitions are either fantastic or altogether incorrect. In the United States, the surface tension is often expressed as a force per unit length at right angle to the surface. It is thus confused xith the inward or molecular pressure, but even then, it is not correct because this pressure is defined as a force per unit area, Le., per centimeter squared, and as such it is of quite a different order of magnitude from surface tension. This has been made clear by the author in a number of papers (J. Phys. Chem. 36, 2406-36 (1932)). If one assumes that the field of force is uniform, the relation between the surface tension, y,and the inward pressure, P , can be expressed as
p = y7p3 where n is the number of molecules per unit volume. Thus, under no circumstances can the surface tension be defined a3 a force per unit length a t right angle to the surface. The considerations stated in this paper apply equally to the interfacial tension. G. ANTONOFF, Department of Chemistry Fordham University Xew York, ?Jew York
NEW BOOKS The ,Methodology of Pierre Duhem. By ARXANDLOWIKGER.56 x 52 in.; 154 pp. Xew York: Columbia Universit:. Press, 1941. Price: $2.25. I n this small book, D r . Lowinger gives a detailed exposition of Duhem’s views on physical experiments, the significance of physical laws, and the nature of physical hypotheses and theories. Although the views of a distinguished physicist should receive respectful consideration, the reviewer is convinced t h a t Duhem’s philosophy of science is quite inadequate; i t assuredly is not in harmony n i t h the prevailing views of twentieth-century scientists. Duhem claimed that he was a physicist, not a philosopher, b u t his methodology shows that he is a mctaphysician malgrl: hi. Even D r . Lowinger, who interprets Duhern’s views so sympathetically in the present book, admits in the final chapter t h a t these views are far from satisfactory. Students who are concerned a t all with the philosophical basis of physical science will find i n this book much t h a t will be of interest. F. H. MACDOUGALL.
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Cellulose Chemistry. By MARKI’LUNGUIAN. 6 x 9 in.; vii 97 pp.; 13 figures. Brooklyn, Ken7 York: The Chemical Publishing Co., Inc., 1943. Price: $2.25. This little book “designed primarily as a brief and up-to-date introduction t o the chemistry of cellulose for non-cellulose chemists,” as stated in the author’s preface, fulfills i t s aim admirably. I t will also be of value t o highly specialized workers who wish brief reviews of the recent developments in other parts of the cellulose field. The chapter on derivatives of cellulose is not very modern, and contains a number of errors. The method described for making guncotton is antiquated, and this substance is not a !‘high explosive.” Moisture-proof cellophane is made from cellulose acetate rather than the nitrate, and flax is “hackled.” There are a few grammatical errors, and one
