78 



II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



acid possesses a cis-cis linkage while linolelaidic acid has a trans-trans con- 

 figuration. The same authors conclude further that these data, in con- 

 junction with results on the Raman spectra, indicate that linolenic acid 

 possesses cis-cis-cis linkages. The glyceryl esters of oleic, linoleic, linolenic, 

 and elaeostearic acids also show absorption maxima at 6 /x, but a much 

 more marked peak occurs at 8.4 /x which is attributed to the oxygen linkage. 

 With gh^ceryltrielaeostearate an additional inflection at 10 m is ascribed by 

 Gamble and Barnett ^^® to the effect of conjugation of the unsaturated 

 bonds. 



Kill) 



Fig. 13. A comparison of the infrared absorption curves for the ethyl 

 esters of oleic (/ ), elaidic (2), linoleic (3), linolelaidic (4), and linolenic (5) 

 acids with that of stearic acid.*^ 



c. Ultraviolet Absorption. Although the saturated fatty acids have 

 no absorption in the region between 400 and 200 m/x, characteristic curves 

 are exhibited by most of the unsaturated acids in this area. There is some 

 indication that the far ultraviolet may be a more satisfactory region for the 

 study of the saturated acids. The investigation in the region of the far 

 ultraviolet is hampered by the difficulty of obtaining simple instruments 

 for such measurements. Most spectrophotometers and other instru- 

 ments for measuring transmission in the ultraviolet record satisfactorily 

 to about 300 m^, and hence the bulk of our information applies to the upper 

 portion of the ultraviolet spectrum. The Beckman spectrophotometer, 

 when used with the hydrogen emission tubes, and in conjunction with 

 quartz cells, can be employed to 210 m^. However, a spectrograph de- 

 vised by Schumann, having highly sensitized photographic plates and an 

 evacuated chamber, allows accurate measurements to wave lengths as 

 short as 120 m^u. By the use of a fluorite optical system, estimations are 

 possible in the far ultraviolet to wave lengths of only 50 m/i. At this short 



