177 



IX. — 0» the Formation of Indigo-blue, Part I. 

 By Edward Schunck, Ph.D., F.R.S. 



IRead April 3rd, 1856.] 



Indigo, one of the most important and extensively used 

 dyes, owes its value entirely to a peculiar colouring matter 

 contained in it, to which the name of indigo-blue or indigo- 

 tine is applied by chemists. This substance has been re- 

 peatedly subjected to investigation, and several distinguished 

 chemists have bestowed their attention and labour upon it. 

 Its properties, composition and products of decomposition, 

 have been so carefully examined, that it may safely be as- 

 serted, that there are few organic substances whose nature is 

 more accurately known than that of indigo-blue. If, how- 

 ever, we inquire into the state of our knowledge regarding 

 the origin and mode of formation of this body, it will be 

 found that our information on this part of the subject is ex- 

 tremely defective. Indigo-blue may be obtained from a 

 variety of plants, which though belonging to the most dif- 

 ferent genera and orders, are rather limited in number. It 

 has sometimes been observed to form in the milk of cows, 

 especially such as have been fed exclusively on saint-foin.* 

 Latterly it has been discovered by Hassallf and others J in 

 human urine, where its occurrence is attributeil to a morbid 



• Ann. do Chira. et de Phys., T. III., p. 269. 



f Philosophical Transactions for 1854. 



X Annalen d. Chem. u. Pharm., 6d. XC, t. 120. 



