74 Dr. Schunck on the Formation of Indigo-blue. 



otlier organic bodies, and to constitute it one sui generis, naturally 

 suggest the inquiry, in what form it is contained in the plants and 

 animals from which it is derived. If it exists ready formed in the 

 indigo-bearing plants, how is it that though, when in a free state, 

 insoluble in water, acids, alkalies, alcohol, and most simple men- 

 strua, it should so easily be extracted from those plants by a mere 

 infusion with cold water ? If it does not pre-exist in the plant, in 

 what state of combination is it contained therein, and what is 

 the nature of the process by which it is eliminated ? The usual 

 method of preparing indigo from the Indigofera consists in steep- 

 ing the plant, especially the leaves, in water, drawing off the 

 infusion, allowing it to undergo fermentation, and then precipi- 

 tating by means of agitation with air and the addition of lime- 

 water. Now it may be asked, is this process of fermentation, 

 which is often very tedious and difficult to manage, essential to 

 the formation of indigo-blue, or is it merely an accidental phse- 

 uomenon attending its preparation ? If it is essential, at what 

 stage of the process is the formation of the colouring matter to 

 be considered as completed ; and is it necessary, as some persons 

 assert, to continue it until actual putrefaction has commenced, 

 or not ? These are points, which, though perhaps of little con- 

 sequence to the dyer and consumer of indigo, are of great interest 

 in a chemical point of view, and are of the greatest importance 

 to the manufacturer of indigo. To the latter it must surely be 

 extremely desirable to know the exact nature of the process on 

 which his manufacture depends, and to ascertain whether this 

 process yields into his hands the whole quantity of the product 

 which the material employed is capable of yielding, and also 

 whether the manner of conducting it is in perfect accordance 

 with theoretical requirements. If, however, we consult the authors 

 who have written on this subject, and the chemists who have endea- 

 voured to elucidate it, we shall obtain very unsatisfactory replies 

 to our inquiries. The views entertained on these different points 

 are either mere surmises, or they are conclusions founded on a 

 limited number of frequently imperfect experiments. The chief 

 cause of our ignorance on these questions is, probably, that the 

 process of manufacturing indigo is one carried on, not in the 

 more highly civilized regions, but in remote parts of the world ; 

 and we are consequently obliged to rely for our knowledge con- 

 cerning it chiefly on the accounts of travellers, who arc usually 

 possessed of merely general information, or of the manufacturers 

 themselves, who are far from competent to give an opinion on a 

 complex orgauo-chemical process. 



Fourcroy, according to Robiquet, considered the formation of 

 indigo-blue to be a result of the process of fermentation em- 

 ployed in its preparation. 



