PHYSICAL PROPERTIES OF FATTY ACIDS 77 



For a further theoretical discussion of the apphcation of spectroscopy to 

 chemical and biological work, the reader is referred to the monographs of 

 Brode-" and of Miller.-^* A useful treatise dealing with spectrophoto- 

 metric instruments was published by Burk and Grummitt.^"^ Hil)ben2'''' 

 has written a monograph on the chemical applications of the Raman ef- 

 fect, and also several excellent reviews on this subject,^^''^^^ which may be 

 of interest to those to whom the monograph is not available. 



b. Infrared Absorption. The infrared region is divided into several 

 areas for convenience. That portion immediately adjacent to the visible 

 end of the spectrum is called the near or short infrared. This includes 

 the part between the wave lengths of 750 and 1000 m^ (7500 to 10,000 A.)."^ 

 The middle region extends from 1000 to 6000 m^u (10,000 to 00,000 A.), 

 while the lower or far infrared region is that portion of the spectrum above 

 0000 mju extending to an upper limit not exactly defined but probably over- 

 lapping the lower Hertzian waves. R. B. Barnes et al.-'^'^ reported on the 

 characteristic absorption of a large number of natural and synthetic organic 

 compounds (including fats and their derivatives) in the infrared. They"^ 

 recently published an excellent monograph entitled Infrared Spectroscopy. 



The curves showing the absorption of the ethyl esters of oleic, linoleic, 

 linolenic, elaidic, and linolelaidic acids in relation to that of stearic acid as 

 determined by McCutcheon et al.^'^ is given in Figure 13, while the results 

 of Gamble and Barnett^^^ on the absorption of the triglycerides of several 

 unsaturated acids in the infrared region are reproduced in Figures 14 and 

 15. 



A marked absorption maximum is noted for the ethyl esters of oleic, lino- 

 leic, and linolenic acids at 6.0 ju (6000 m^i), while elaidic and linolelaidic 

 esters show only a slight inflection at this wave length. On the basis of 

 theoretical considerations, it is beheved that the absorption in this area 

 is associated with a cis arrangement, which would explain the absence of 

 absorption by the trans isomers, elaidic and linolelaidic acids. Mc- 

 Cutcheon et al.^^ suggest also that the absorption curves prove that linoleic 



2*' W. R. Erode, Chemical Spectroscopy, 2nd ed., Wiley, New York, 1943. 



^^ E. S. Miller, Quantitative Biological Spectroscopy, Burgess, Minneapolis, 1939. 



2"' R. E. Burk and O. Grummitt, eds., Major Instruments of Science and Their Applica- 

 tion to Chemistry, Interscience, New York, 1945. 



"" J. H. Hibben, The Raman Effect and Its Chemical Applications, Reinhold, New York, 

 1939. 



2" J. H. Hibben, Chem. Revs., 13, 345-478 (1933). 



272 J. H. Hibben, Chern. Revs., 18, 1-232 (1936). 



2" One micron {y.) is equal to 0.001 mm. One millimicron (m^i) equals 0.001 m, or 

 0.000,001 mm. One angstrom unit (A.) equals 0.1 niM or 0.000,000,1 mm. 



27^ R. B. Barnes, U. Liddel, and V. Z. Williams, Ind. Eng. Chem., Anal. Ed., 15, 659- 

 709 (1943). 



"* R. B. Barnes, R. C. Gore, U. Liddel, and V. Z. Williams, Infrared Spectroscopy, 

 Reinhold, New York, 1944. 



2"« D. L. Gamble and C. E. Barnett, Ind. Eng. Chem., 32, 375-378 (1940). 



