60 
MADDER DYES FROM COAL. 
By EDWARD DIVERS, M.D., E.C.S. 
!HE beautiful dye-stuffs produced from coal-tar have all 
proved to be until recently such as were unknown bodies 
before they were obtained from this source. A new interest 
has now, however, been imparted to the colour-producing pro- 
perties of coal-tar by the transformation of one of its consti- 
tuents into one of the most important and beautiful vegetable 
dyes that are known — the dyeing matter derived from the 
madder ( Rubia tinctorum ). As the reader can hardly be as- 
sumed to be very familiar with what has been ascertained 
respecting the production of dyes from the madder-plant 
itself, it will be w.ell to consider very briefly this production, 
which, though of some complexity, and still imperfectly com- 
prehended, possesses considerable scientific as well as practical 
interest. 
When powdered madder-root is spread upon an iron plate 
and cautiously heated so as to avoid scorching it, small orange- 
coloured crystals are seen to form upon its upper surface, which 
are the substance that imparts to the root its valuable dyeing 
power. This substance, discovered by Robiquet, is called 
alizarin , from alizarin the name by which madder is known 
in the Levant. 
Alizarin, like indigo, appears, from the microscopic observa- 
tions of Decaisne, not to exist ready formed in the juices of 
the living plant. The cells of the root are found to be filled 
with a yellow substance which increases in quantity with the 
age of the plant; and this substance gives rise to the true 
colouring matter when the juice is exposed to the air. De- 
caisne’s observations were, however, disregarded by the chemists 
who investigated madder until Higgins* drew attention to 
them again, and, by some very simple and admirably devised 
experiments, established their accuracy. From these experi- 
* In a paper read by him at the British Association in 1848. u Philoso- 
phical Magazine,” XXXIII. 282. 
