lOG 



II. CHEMISTRY OP FATTY ACIDS AND GLYCEROL 



in which AI is the molecular weight, 7 is the surface tension in dynes per 

 square centimeter, D is the density in the liquid state, and d the density in 

 the vapor state. This calculation gives the value of P, which is the para- 

 chor. Since the value of the parachor does not vary with temperature, it 

 provides a simple means of expressing the relationships between surface 

 tension, density, and molecular weight. 



Table 38 



Surface Tension, Interfacial Tension and Parachor of Some Fatty Acids and 



Their Esters" 



Surface tension Interfacial 



against air, tension against 



Compound dynes/cm.'' water, dynes/cm. * Parachor* 



Heptanoic acid 28.312" 7.00'-« — 



Caprylic acid 28.82«-i 8.22«i — 



Undecanoic acid 30 . 6i^ 10 . 14« — 



Laurie acid — — 522 . 5 



Palmitic acid — — 668 



Stearic acid 26.99^ — 777.79 



26.42^5 _ 778.87 



Behenic acid 37.779" — 950.07 



37.6P5 — 951.36 



Oleic acid 32 . 50^" 15. 592" — 



27.9490 — 765.07 



27.5295 — 766.93 



Elaidicacid 26.569" — 760.44 



26.3195 — 764.93 



Erucicacid 28.569" _ 932.40 



27.779* — 938.91 



Brassidic acid 27.409" — 929.20 



27.2895 — 934.36 



Ricinoleic acid 35.811' 14.25" — 



Ethyl caproate 25. 81^" 19.802" — 



Ethyl nonanoate 28 . 04^" 23 . 88"" — 



Ethyl oleate — 21.342" — 



" Data are assembled from K. S. Markley, Fatty Adds, Interscience, New York, 1947. 

 E. L. Lederer, Seifensieder-Ztg., 57, 575-576 (1930); Chem. Ahst., 24, 5549 (1930). 

 G. B. Semeria and G. Ribotti-Lissone, Gazz. chim. ital., 60, II, 862-866 (1930); Chem. 

 A6.s<., ^5, 1800(1931). 



* The superscripts are the temperatures at which the determinations were made. 



'^ .\lthough the parachor is independent of temperature, the calculated values relate 

 to the temperatures at which surface tension was determined. 



Surface tension may be defined as a measure of the attractive forces of 

 molecular origin which tend to keep a liquid together. They are exerted 

 only over very short distances. During evaporation of a liquid, these at- 

 tractive forces must be overcome; the heat required to produce evaporation 

 is considered to be a measure of such a force. 



As a result of surface tension, drops of a liquid tend to contract to a form 



