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A Paper was read “ On Some Products Derived from 
Indigo Blue / 5 by Dr. E. Schunck, F.R.S., Vice-President. 
By his experiments on the formation of indigo blue, an 
account of which was laid before the Society several years 
ago,* the author was led to make some inquiries regarding the 
processes employed in tropical countries for the production of 
indigo from plants. All authorities, it appears, agree that 
the process of fermentation, which is the one usually adopted 
for the purpose of extracting the colour, requires to be 
conducted with the greatest care in order to lead to a successful 
result. Unless certain precautions are adopted the colouring 
matter may be entirely lost. This phenomenon may be easily 
accounted for. Though indigo blue, when once formed is a 
very stable body, the substance existing in the cells of the 
plant from which it originates and which the author terms 
Indican , is decomposed with the greatest facility, indigo 
blue being only one of its products of decomposition, which 
may be formed or not, according to the nature of the process 
employed. 
There are, however, other facts connected with this subject 
which cannot so easily be explained. It is well known to 
those dyers who employ the so-called woad vai , in which the 
reduction of the indigo blue is effected by means of various 
organic matters, such as woad, madder, and bran, together 
with lime, that if the process be not carefully managed it 
may change its character entirely — a change which results in 
the total destruction or disappearance of the colouring matter. 
This phenomenon cannot be explained in accordance with 
what is at present known regarding indigo blue, which is 
considered by chemists to be a body of such a stable character 
* See Memoirs, Yol. XXV., p. 181. 
