248 MESSRS. DAL£ AND SCHORLEMMER ON AURIN. 



great advantage in these instruments is the very small 

 amount of substance required to give the necessary 

 deflection. I have found in practice that 0*5 to 2 

 grammes is quite sufi&cient, the amount, of course, 

 varying with the size of the instrument. 



XXXI. On Aurin. 

 By R. S. Dale, B.A., and C. Schorlemmer, F.R.S. 



Bead April 2nd, 1878. 



In a paper read before this Society on 31st October, 1871, 

 we gave a short account of this colouring- matter, which 

 was discovered by Kolbe and Schmitt in 1861. We 

 showed that the commercial product, which is called aurin 

 or corallin, and is obtained by heating phenol with 

 sulphuric acid and oxalic acid, is a mixture of different 

 bodies, from which we isolated a colouring-matter which 

 crystallized exceedingly well and for which we retained 

 the name of aurin ■^. The analysis of this body gave 

 numbers agreeing with the formula Cj.oH14.O3, from which 

 we concluded that it was produced by the action of nascent 

 carbonic oxide on phenol : — 



SC^H^O + 2C0=C,,H.40, + 2H,0. 

 We further showed that aurin, when treated in an al- 

 kaline or acid solution with zinc-dust, combines, like most 



* A full account of this investigation is found in Journ. Chem. See. (2) 

 xi. 434. 



