20 MESSRS. DALE AND SCHORLEMMER ON THE 



talline compound^ whicli we intended to examine more 

 closely. We have since found that this body is identical 

 ■with a compound which Grabe and Caro^ obtained by the 

 direct union of aurin and acetic anhydride and having the 

 formula C.^H.^Oj + C^H^O,. 



We also mentioned that the purification of this substance 

 was found to be beset with several difficulties. The cause 

 of this was found out after some trouble -, but at the same 

 time we were rewarded by the discovery of a series of re- 

 markable bodies^ consisting of combinations of aurin with 

 mineral acids. 



These salts, as we may call them_, are beautiful bodies, 

 crystallizing exceedingly well ; and although some of them 

 are decomposed by water, they are very stable in dry air. 

 To their discovery we were led by the following ob- 

 servations. 



On heating aurin with glacial acetic acid and acetyl 

 chloride, the crystals lose at once their steel-blue lustre 

 and assume a pale red colour. To obtain the compound 

 thus formed in a pure state, acetyl chloride was added to 

 a saturated solution of aurin in acetic acid. The hquid 

 assumed at once a much lighter colour ; and soon pale red 

 needle-shaped crystals having a diamond lustre separated 

 out. On recrystallizing these repeatedly from alcohol, we 

 obtained oblong six-sided plates, which, as analysis showed 

 were pure aurin, 



On treating the original crystals with water, they became 

 dull and brownish red, the solution containing acetic and 

 hydrochloric acids. It therefore seemed not improbable 

 that an additive product of aurin and acetyl chloride had 

 been formed, containing, however, also acetic acid, as a 

 superficial examination showed that the liquid contained, 

 to one molecule of hydrochloric acid, much more than one 

 * Ber. deutsch. ohem. Ges. xi. p. 1122. 



