PHYSICAL PROPERTIES OF FATTY ACIDS 101 



oleates at several temperatures, reported by Keffler and McLean, ''^•^ are 

 given in Table 34. 



Table 34 

 Densities op Oleic Acid and Alkyl Oleates at Different TEMPEBATaREs" 



« L. Keffler and J. H. McLean, /. Soc. Chem. hid., 54, 178-185T (1935), p. 182. 



(a) Specific Volumes of Fatty Acids. One of the constants which can be 

 deduced from density measurements is the specific volume. This may be 

 defined as the reciprocal of the density. The specific volumes of the satu- 

 rated fatty acids from Cg to C12 were determined at different temperatures 

 by Garner and Ryder, ^** who employed the air-thermometer method. 

 The values for the solid and liquid acids at their melting points were as 

 follows: Cs, 0.9737 and 1.0925; C9, 1.0104 and 1.0966; Cio, 0.9870 and 

 1.1169; Cn, 1.0121 and 1.1206; and C12, 0.9971 and 1.1403. There were 

 changes in molecular volume at the melting point in A cc. per gram mole 

 as follows: Cg, 17.51; C9, 13.95; Cio, 23.24; Cn, 20.68; and C12, 29.07. 

 As would be expected, the specific volume increases with the lengthening 

 of the fatty acid chain and with a rise in temperature. 



(6) Molar Volumes of Fatty Acids. The molar volume is defined as the 

 volume occupied by one gram mole of the substance. It is readily calcu- 

 lated by dividing the molecular weight of a substance by its density. 

 When used for the acids in the solid state, it furnishes information on the 

 cross-section area of the unit cell of the crystal, especially when used in 

 conjunction with x-ray measurements. 



Pauly^^^ found that the molar volume of the lower fatty acids increases 

 by an average of 22.3 cc. per gram mole in the liquid state for each CH2 

 group added, while Garner and Ryder^*^ have given the figure as 16.8 cc. 

 Alternation in the values occurs in the solid but not in the liquid state. 

 Since a change in cross section was shown to be a non-alternating property, 

 it has been concluded that variations in molecular volume are to be as- 

 cribed exclusively to alterations in chain length. The regularity of the 

 increment in the molar volumes as the fatty acid chain is lengthened is in- 



'" L. Keffler and J. H. McLean, J. Soc. Chem. Ind., 54, 178-185T (1935). 

 3" W. E. Garner and E. A. Ryder, J. Chem. Soc, 127, 720-730 (1925). 

 3« H. Pauly, Z. anorg. allgeni. Chem., 119, 271-291 (1921). 



