168 



Prof. J. Dewar. 



[Feb. 12, 



bine with it, forming a reddish- violet solid. If the excess of chloride 

 of ethyl containing the uncombined leucoline is distilled in a current 

 of steam, this portion of the base now yields a crystalline chromate. 

 Similarly, the original leucoline heated in sealed tubes to a tempera- 

 ture of 170° C. with chromic acid in the proportion of 10 grms. to 

 5 cub. centims. of the base, gave, after separating the oxide of chro- 

 mium, on distilling caustic potash, the base yielding the crystalline 

 chromate. The alkaline fluid on evaporation to dryness, and heating 

 with soda ime, gave a little pyrrol, but no aniline. The alkaline solu- 

 tion distilled with excess of sulphuric acid gave volatile organic acids. 

 The ordinary leucoline treated directly with iodide of ethyl gave a red 

 viscid mass, containing yellow crystals, which may be separated by 

 successive washings with alcohol . When this iodide of ethyl leucoline 

 was distilled, the free base yielded the crystalline chromate ; whereas 

 the leucoline separated from the oily chromate, when heated with 

 iodide of ethyl, gave an intense red-coloured fluid, in which a few 

 crystals appeared after standing for a week or two. 



It thus appears by the three methods detailed above, that ordinary 

 leucoline is a mixture of two isomeric bases ; and that samples of the 

 tar product may differ considerably in properties. 



We can thus easily explain how Hofmann obtained on one occa- 

 sion a crystalline chromate from the tar bases, which led him to infer 

 that the substance was identical in properties with that derived from 

 the decomposition of the cinchona alkaloids ; whereas Greville 

 Williams, working upon a different specimen, could obtain- nothing 

 but an oily uncrystallisable salt. 



In reality both experimenters described the properties of different 

 specimens of the bases. 



Oxidation of Leucoline. 



Many attempts to increase the yield of leucoiinic acid, by varying 

 the proportions and temperature of the reacting bodies, led to the 

 following results. 



The greatest amount of acid is obtained when one part of the base, 

 dissolved in the form of neutral sulphate, is treated with 2-J- times its 

 weight of permanganate of potash dissolved in boiling water, the 

 oxidising agent being carefully added to the salt of leucoline. If the 

 action is allowed to proceed in the cold with about four parts of the 

 permanganate to one of base, there is no leucoiinic acid formed, all the 

 higher boiling point bases, belonging either to the tar or cinchona 

 series of bases, yielded acid derivatives on oxidation, which, on distil- 

 lation with soda-lime, gave aniline when the above plan was adopted ; 

 if this was not done, the chief product was a member of the pyridine 

 series. This explains why von Dorp, Koenigs, and others have found 

 only pj^ridine dicarbonic acid without any trace of leucoiinic acid. 



