Robektson. — Molecular Complexity of Fatty Acids. 455 



Table I. 

 Stearic Acid* (molecular weight, 284). 



1. Weight of phenol = 106 grams. 



Fall in F.P. (d). Weight of Acid. Molecular Depression. 

 •59° -2290 76-5° 



■395° -1736 68-5° 



•56° -2906 58° 



i.e., association increases yVs-sV for a fall of 1'07° (~ 5 o 9 ~+ - 395 

 + - 5 2 6 -) .*. increases 147 per cent, for a fall of 5°. 



2. Weight of phenol = 14-5 grams. 



Fall in F.P. (d). Weight of Acid. Molecular Depression. 

 •40° -2168 76° 



■31° -1888 67° 



•22° -1454 62° 



•53° -3594 60° 



i.e., association increases y 1 ^— eT> f° r a ^1 °f "99° .\ increases 

 135 per cent, for a fall of 5°. Mean increase, 141 per cent. 



The molecular depression is calculated from the equation 

 D = ^tt-^- — where W and m are the weights of the 



phenol and stearic acid respectively. 



The experimental results are given in detail in Table II. 

 A number of these results are represented graphically, the 

 molecular depression being plotted against the concentration 

 (see Plates XLVIII. and XLIX.). The different acids will be 

 considered under the following heads : — 



1. The fatty acids. 



2. The mono-, di-, and tri-substituted acetic acids where 

 the substituents are phenyl, alkyls, and halogens. 



3. The dicarboxylic acids. 



4. Oxy and nitroso acids. 



5. The substituted arnido acids. 



6. Acids whose molecular depression increases with the 

 concentration. 



1. (a.) The Normal Fatty Acids (Nos. 1-8, Table II.).— The 

 rate of association alternately increases and diminishes as the 

 series is ascended, each of the even members associating more 

 rapidly than either of the two contiguous odd acids. If 

 alternate members are considered — e.g., the even — it is found 

 that the rate slowly decreases, reaches a minimum probably 

 at C 6 , and then increases extremely rapidly. From con- 

 siderations in the next paper, where cases of this nature 



* Owing to its slight solubility a depression of only about 1£° could 

 be reached. 



