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XVII. On the formation of Rosolic Acid and Rosaniline. 

 By H. Caro*. 



IT has been recently shown by Wanklyn and myselff, that 

 rosolic acid may be obtained from rosaniline by the same 

 method as that by which phenol is derived from aniline. This 

 observation indicates the existence of a common hydrocarbon 

 skeleton in rosolic acid and rosaniline, and exhibits the dye- 

 forming acid and the dye-forming base as members of the same 

 natural family. 



From this point of view it seemed that a comparison and 

 study of the various methods of preparing these substances was 

 calculated to throw light upon the constitution of both of 

 them. 



Rosolic acid is formed in a set of reactions J hardly less 

 numerous and interesting than the variety of processes devised 

 for the production of rosaniline. Discovered in 1834 by Runge§ 

 in coal-tar, and obtained from the residues of the preparation 

 of carbolic acid by treating them with lime, its beautiful rose- 

 coloured compounds with alkalies and " appropriate mordants/' 

 attracted the attention of this chemist, to whom we also owe the 

 discovery of carbolic acid and aniline. 



Runge considered rosolic acid to be a true colouring-matter 

 capable of forming red pigments and lake-colours, rivalling in 

 beauty those produced by safflower, cochineal, and madder. In 

 fact, rosolic acid, or more correctly the rosolates, were the first 

 remarkable colouring-matters derived from coal-tar. Curiously 

 enough, notwithstanding its striking properties, rosolic acid was 

 lost sight of by chemists, and even its existence doubted, until 

 Tschelnitz || noticed its formation during the prolonged contact 

 of carbolic acid with lime, and, following the indications given 

 by Runge, confirmed his observations upon this colouring- 

 matter. 



A more complete investigation was made by H. Miiller^j", who 

 found that a quantity of " crude carbolate of lime, which had 

 been left for many months in a warm drying-closet, was entirely 

 converted into a red substance, which on treatment with water 

 gave a beautiful dark-red solution." 



About the same time, or a little earlier, Angus Smith** 



* Communicated by the Author, 

 f Proc. Roy. Soc. vol. xv. p. 210. 

 J E. Kopp, Moniteur Scientif. vol. iv. p. 118. 

 § Pogg. Ann. vol. xxxi. p. 76. 

 || Wien. ATcad. Ber. vol. xxxih. 1857, p. 269. 

 % Chem. Soc. Journ. 1858, vol. xi. 

 ** Mem. of the Lit. and Phil. Soc. of Manchester, 1st Dec. 1857. 



