D. CHEMISTRY AND METALLURGY. 229 



ON A NEW COLORING MATTER CALLED EOSIN. 



In 1871 Baeyer observed that when pyrogallol was heated 

 with phthalic oxide under such circumstances that water 

 was abstracted, a peculiar body resulted, which was brown- 

 red in color with a yellowish -green lustre, and which dis- 

 solved in alkalies with a magnificent blue color. To this 

 substance he gave the name Gallein. A short time afterward 

 he observed that this reaction was entirely general, and that 

 whenever a phenol of any atomicity was heated in this way 

 in presence of a dibasic organic acid, a coloring matter was 

 the result. The body thus obtained gave rise to two deriva- 

 tives ; one of which is its anhydride, and the other its reduc- 

 tion product. For the coloring matter itself Baeyer proposes 

 the termination ein ; and for its reduction product, which is 

 colorless, in. Thus with phthalic acid and phenol, for ex- 

 ample, there is a phthalin and a phthalein of phenol. Among 

 the various phenols which were thus treated w 7 ith phthalic 

 oxide was resorcin, one of the three diatomic phenols. Of 

 course the products were a phthalin and a phthalein of re- 

 sorcin. The phthalein of resorcin was obtained in yellow 

 flocks which dissolved in ammonia, giving a red solution, 

 which had such a magnificent green fluorescence as to secure 

 for it the separate name fluorescein. It would seem as if a 

 coloring matter like this, prepared from substances exceed- 

 ingly rare, and obtained only in minute quantities by long 

 and tedious chemical processes, could never become an ar- 

 ticle of commerce. But early in the present year Hofmann 

 had placed in his hand a new coloring matter, which had 

 only a few months before come into practical use. This 

 new coloring substance had the name Eosin, a name given in 

 allusion to the beautiful red color of its aqueous solutions, 

 recalling that of the morning dawn. Upon investigation, 

 eosin turned out to be a derivative of the remarkable color- 

 ing matter which Baeyer had called fluorescin. It was the 

 potassium salt of tetrabrominated fluorescin, or, what is the 

 same thing, of the phthalein of dibrom-resorcin. It is pre- 

 pared commercially at the Baden Aniline Works, by Caro. 

 Baeyer proposes the following test for it : A portion of the 

 coloring matter is agitated with water and sodium amalgam 

 at a gentle heat. The solution is soon decolorized, the bro- 



