Manchester Memoirs, Vol. xlvii. (1903), No. 6. 5 



I, 2, 4, trihydroxyanthraquinone, and devised an ingenious 

 method for showing the presence of small quantities of 

 alizarin in mixtures of this substance with purpurin. 

 This consists in exposing the alkaline solution of the 

 mixture to the air, when the purpurin is rapidly oxidised 

 and destroyed. Any alizarin present remains unchanged, 

 and can be readily detected by examining the absorption 

 spectrum of the solution. 



Schunck and Roemer were also the first to show that 

 purpurin, when heated gradually to 300°, is converted, by a 

 remarkable process of reduction, into chinizarin or 1,4, 

 dihydroxyanthraquinone. 



At as recent a date as 1893 Schunck again took up 

 the investigation of madder root, and in a paper published 

 in conjunction with Marchlewski he describes the isolation 

 of a new glucoside of the formula C^HaoOg, which he 

 called rubiadinglucoside. This new glucoside crystallises 

 in yellow needles, and is hydrolysed by dilute acids with 

 formation of rubiadin and glucose. 



C21H20O9 + H2O = CisHioOi + C6Hl206. 



The constitution of rubiadin was also carefully investi- 

 gated, and it was found that this substance is a di- 

 hydroxymethylanthraquinone or methylpurpuroxanthin 

 of the formula 



CO OH 



qh/ Nqh^oh 



^CO'^^ CHs 



We may next notice the important researches which 

 Schunck carried out on the nature of the constituents of 

 the plants Indigofera tinctorm, Isatis tinctoria and Poly- 

 gonum tinctoriuni. All of these yield indigo when their 

 leaves are macerated with water in contact with air, and 

 the first-mentioned is tjrown in India and China in 



