229 



differences in the velocity of formation or decomposition of com- 

 pounds of the types Af a.nd.A'f. 



Marckwald and MacKenzie 1 ) succeeded, after a number of 

 unsuccessful experiments of other investigators 2 ), in demonstrating 

 that, if x-ethoxy-propionic acid, racemic mandelic acid, etc., be com- 

 bined with l-menthol to form an ether, and if the reaction be stopped 

 after a certain lapse of time insufficient to complete the change, 

 the acid set free from the ether by saponification was endowed 

 with rotatory power. 



The same appeared to be the case if racemic mandelic acid were 

 heated with l-menthyl-amine, so as to form the corresponding amide. 

 In the portion which was not changed into amide, an excess of 

 the laevogyratory acid was found to be present. It should be noted, 

 that the compound which was formed more rapidly by etherification, 

 appeared also to be more rapidly decomposed by saponification, 

 which is in accordance with the fact that we have to deal here with 

 a reversible action, leading to a state of dynamical equilibrium. 



This fission of the racemoid is of course only a partial one. We 

 shall return to this subject in the next chapter, when we are 

 dealing with the problem of asymmetrical synthesis in general. 



12. Till now we have dealt only with those cases, in which 

 either an externally compensated mixture of both components or a 

 true racemic compound of them was present. 



However, another difficulty for obtaining the two components 

 in a perfectly pure state, besides the obstacles already mentioned, 

 is this, that the two components may occasionally form together an 

 uninterrupted series of mixed-crystals, this series behaving, therefore, 

 as a single solid phase of continually varying composition. 



This phenomenon discovered in 1897 by Kipping and Pope 3 ) in 

 the case of some camphor-deYivates, was named pseudo-racemism. 

 Since Bakhuis Roozeboom 4 ) in 1899 published the paper in 

 which he indicated the way to discriminate with certainty the three 

 classes: racemic compounds, externally compensated mixtures, and 



!) W. Marckwald and A. MacKenzie, Ber. d. d. Chem. Ges., 32, 2130, (1899). 

 34, 469, (1901); W. Marckwald and R. Meth, Ber. d. d. Chem. Ges., 38, 

 801, (1905). 



2 ) L. Simon, Bull, de la Soc. Chim., (3), II, 760, (1894); P. Frankland and 

 Th. S. Price, Journ. Chem. Soc. London, 71, 253, (1897); etc. 



3 ) F. S. Kipping and W. J. Pope, Journ. Chem. Soc. London, 71, 973,989, (1897). 

 *) H. W. Bakhuis Roozeboom, Zeits. f. phys. Chemie, 28, 494, (1899). 



