66 DR. EDWARD SCHUNCK ON SOME 



is scarcely more easy to believe that the cemetery-beds 

 and those of the higher land are merely portions of a de- 

 posit under similar conditions on a rising coast, the incline 

 being not less than 600 feet in 6 miles. Can there have 

 been a local alteration of level ? 



III. On some Products derived from Indigo-blue. 

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



Bead January loth, 1865. 



My experiments on the formation of indigo-blue, an account 

 of which I had the honour of presenting to this Society 

 several years ago, led me to make some inquiries regarding 

 the processes employed in tropical countries for the pro- 

 duction of indigo from the various plants yielding that 

 dye-stuff. I found that all the authors who have written 

 on the subject agree in affirming that the process of fer- 

 mentation, which is the one usually adopted for the purpose 

 of extracting the colour from the plant, requires to be con- 

 ducted with the greatest care, in order to yield a successful 

 result. Unless certain precautions are adopted, a product 

 of very inferior quality will be obtained ; in some cases, 

 indeed, the colouring matter is entirely lost. This will 

 not be surprising to any one who considers that though 

 indigo-blue, when once formed, is a very stable compound, 

 the substance existing in the cells of the plant from which 

 it originates, and which I have named indican^ is decom- 

 posed with the greatest facility in various ways ; that indigo- 

 blue is only one of its products of decomposition, and may 

 be formed or not, according to the nature of the process to 

 which it is submitted. With this sufficiently obvious ex- 



