Eobertson. — Molecular Complexity of Fatty Acids. 461 



If, on the other hand, two molecules united through the 

 nitroso groups a dibasic acid would be formed, and then the 

 association should be expected to increase with the depression 

 of freezing-point. 



5. Substituted Amido Acids. — The a amido acids are 

 characterized by extreme insolubility in phenol. First it was 

 thought that this was due to the internal combination of the 

 acid and basic parts of the molecule, the constitution of these 

 acids then becoming 



I I 



X • CH • C • O • NH 3 



This, however, is rendered improbable for the following 

 reasons : — 



(a.) In the case of amidosuccinic acid one carboxyl group 

 should become neutralised, forming a monocarboxylic acid, 

 which would then dissolve. This substance, however, is 

 extremely insoluble. 



(b.) Anilidoacetic acid has a considerable rate of associa- 

 tion, whereas if the carboxyl group were neutralised this 

 would hardly be expected. 



Hippuric (i.e., benzoylamidoacetic) acid is characterized 

 by its great rate of negative association. (It must be remem- 

 bered, however, that the total depression is only a little 

 above 1°.) The slight solubility cannot be the cause (for 

 anilidoacetic-acid associates). It is well worth remarking, 

 however, that the saturated solutions of these two acids have 

 the same molecular depression, 71, which is about the mean 

 value for the so-called constant. 



6. Acids ivhose Molecular Depression increases with the 

 Concentration. — Levulinic acid gives the abnormally high 

 value 82 for the molecular depression. This, however, is 

 probably correct. The acid obtained by fractionation under 

 reduced pressure gave the value as 75. On solidifying this in 

 a freezing mixture and separating the solid from the liquid 

 the former gave the mean value 82. 



In 1887 Bredt* gave the constitution of levulinic acid as 



CH 

 CH 2 C (CH S ) • OH 



CO— o 



Annalen," 236, 225. 



