RECENT RESEARCH ON INDIGO 1 



By H. H. ROBINSON, M.A., F.I.C., F.C.S. 



Indigo is a blue dyestuff owing its tinctorial properties chiefly 

 to a chemical substance known as " indigotin " ; of this Bengal 

 indigo contains about 60 per cent., and of the other ingredients 

 some are considered to have a beneficial effect when indigo is 

 used as a dye. Indigo is obtained from a plant (Indigofera 

 tinctoria, Linn.), which however does not contain indigotin but 

 a colourless glucoside " indican," which on hydrolysis yields dex- 

 trose and indoxyl ; the latter by oxidation becomes converted into 

 indigotin. In the process of manufacture the leaves are steeped' 

 in water and the liquid obtained is run off and submitted to the 

 oxidising action of the air, whereby indigotin is formed as an in- 

 soluble blue precipitate; this is removed, dried and sold as indigo. 

 Indigo has long been known, mention of it occurring in the 

 works of Pliny and Dioscorides, who both wrote about 100 a.d. ; 

 the names they used, " Indicum " and " 'IvSlkov" imply that it 

 was of Indian origin. The importation of indigo in large 

 quantities into Europe from the East began about the com- 

 mencement of the seventeenth century, and it became a serious 

 rival to woad, a blue dyestuff prepared from the woad plant 

 (/satis tinctoria, Linn.), which also contains a substance yielding 

 indigotin. The use of indigo provoked the opposition of 

 powerful interests in Europe that were concerned in the 

 production of woad, but after a struggle it succeeded in dis- 

 placing the use of the latter; in the closing years of the 

 nineteenth century, however, it has been threatened in its turn 

 by artificial indigotin produced from coal-tar products in the 

 laboratories of Germany. 



1 Report to the Government of India, containing- an account of the Research 

 Work on Indigo performed in the University of Leeds, 1905 — 1907. By. W. Popple- 

 well Bloxam, B.Sc. (Lond.), F.C.S., F.I.C. With the assistance of S. H. Wood, B.Sc. 

 (Lond.) ; I. Q. Orchardson, B.Sc. (Aberdeen) ; R. Gaunt, Ph.D. (Berlin), M.Sc. 

 (Leeds); and F. Thomas, B.Sc. (Mane), F.C.S. ; and under the general super- 

 vision of Mr. A. G. Perkin, F.R.S., F.R.S.E., F.I.C, of the University of Leeds. 

 [Pp. 117.] (Published by Order of His Majesty's Secretary of State for India in 

 Council, 1908.) 



575 



