454
ROBERT B. ANDERSQK AXD H. H. ROWLEY
Tno separate and distinct curves, approximating linearity, are obtained only a t low temperatures 71 hen the miscibility diagram is such that the phase-boundary lines do not form a continuous curve and are approximately linear in form. By suitable mathematical manipulation of the three equations proposed (1;) to describe the system n-heptane-methylcyclohesane--anilinea t 25.0°C., the following relation may be derived:
in which all of the symbols on the right-hand side of the equation are constant. As rn is one of the variables, the above result is anomalous. This anomaly is probably due to the inadequacy of the relations proposed to account accurately for the system. This research was made possible through the kind cooperation of Liessra. Trinidad Leaseholds Limited, who hare retained one of us (B. de B. Darment) in their employ. We acknon-ledge gratefully their permission to publish these results. REFERESCES (1) BRANCKER, A . V., HUXTER,T. G., ASD Naslr, A . W.: Ind. Eng. Chem., And. Ed. 12, 35 (1940). (2) Inlernalional Critical Tables, Volume 111, page 398. McGraw-Hill Book Company, Inc., Yew York (1925). (3) SHERWOOD, T. Iheequations:
+ COz + CO 2HCOOH -+ H,O + COz + HCHO HCOOH
-+
Hz
HCOOH -+ H20
The result,s indicatr that, other primary reactions must occur t,o a slight extent. The rate of propene formation was of the first order, and the experimental activation energies for this step were calculated to be 39,660 cal. for n-propyl forinatr and 44,230 cal. for isopropyl formate. The velocity constants for these rcact,ions can he expressed by the following equations: n-Propyl formate: Tsopropyl form&:
= 2.94 X 10Qe-39'860'RT k = 2.47 X 10'2e-44'230'n2
12
R.EFERENCES (1) A N D E R ~ O N ROWLSY, , .\ND MAKDNS:Proc. Iowa Acntl. Sci. 49, 291 (1042). (2) RILGERAXD HIBBERT:J. Am. Chem. SOC.69, 823 (1936). (3) J%URXH.AM . i ~ i 1'w.s~: i J. Am. Chem. Sac. 64, 1404 (1012).
DEFINITION OF SURFACE TENSION
463
(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 T H E 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 a t variance with the 'Received March 1,1943.
