6 PerkiN, Chemical Researches of Edivani ScJiunck. 



immense quantities, and serves as the source of nearly 

 all the natural indigo which comes into the market. 



It was known from very early times that indigo is 

 not contained as such in the leaves of Indigofcra iincloria, 

 and that, in order to produce indigo, it is necessar}- that 

 the extract of the leaves shall undergo oxidation. In 

 order to explain this, it was at first supposed that the 

 leaves contained indigo white, and that this on oxidation 

 was then converted into indigo. Schunck^ however, 

 showed that this could not be the case, because the clear 

 aqueous extract of the leaves which deposits indigo on 

 standing in the air is acid, and indigo white is only 

 soluble in alkaline aqueous solutions. On investigating 

 this matter, Schunck succeeded, in 1853, in extracting 

 from Isatis tinctoria an unstable syrupy glucoside which 

 he named zndican, and which, when warmed with dilute 

 acids in contact with air, readily yielded indigo. 



In 1900 Hoogewerff and H. ter Mculen succeeded in 

 obtaining the glucoside in a crystalline condition, bat 

 Marchlewski and Radcliffe, in 1898, were the first to give 

 a satisfactory explanation of the composition of this 

 glucoside and its behaviour with acids. 



There can be little doubt that Schunck's indican is, 

 in reality, a glucoside of indoxyl, and that, on hydrolysis, 

 it is first converted into glucose and indoxyl, and this 

 latter in contact with air is at once oxidised to indigo. 

 These changes may be represented thus : 



CuHiTNOc + H2O = CeHiaOe + CsHvNO (indoxyl) 

 2C8H7NO + O2 = 2H,0 + Ci,H,oN,02 (indigo). 

 In connection with his researches on indigo, Schunck 

 cultivated for some years the plant Polgyomim tinctorium 

 in his garden at Kersal, and a short time since he published 

 a very interesting monograph entitled ' The action of 

 reagents on the leaves of Folygonuju tinctorium! This 



