XXIX.—On the Colouring Matter of the Morinda citrifolia. By Tuomas 
ANDERSON, Esq., M.D. 
(Read 17th April 1848.) 
_ The chemistry of the colouring matters has, perhaps, scarcely as yet met with 
the extended and complete investigation which the importance of the subject, in 
a theoretical and practical point of view, appears to deserve. The attention of 
chemists has been almost exclusively directed to the study of a comparatively 
small number of these substances, such as indigo, logwood, and the colouring 
matters of the lichens, which have been well and completely investigated; while 
the remaining, and by far the more extensive class, has received only a very par- 
tial and imperfect examination. To the latter, however, belong some of the most 
important of our dyes ; and among others, the most valuable and indispensable 
of all, madder namely, the chemistry of which forms a problem as yet very far 
from being solved, but which chemists have shewn little disposition to submit to 
a thorough and searching investigation ; and this disinclination seems to con- 
tinue, notwithstanding that ground has been broken on the subject by the im- 
portant observations of RopiqurT, KunLMANN, RunGs, and others, which, though 
extremely incomplete, serve at least to indicate the importance of the results it is 
likely to afford, and to clear away the preliminary difficulties by which the com- 
mencement of such an investigation is surrounded. 
But madder is only one member of an extensive class of dye-stuffs, each of 
which contains one or more colouring matters, the chemical constitution and rela- 
tions of which are almost entirely unknown; and it may seem surprising that, 
with the important results obtained from those already examined before them, 
chemists should not have attempted to work out more completely than has yet 
been done, the rich mine of facts which they present, and the full exploration of 
which is equally important to theoretical chemistry and to its practical applica- 
tions. The reason, however, in all probability is, that they have been deterred 
from the investigation by the small quantity of actual colouring matters which 
most of these substances contain, and the tedious and complicated processes re- 
quisite for their preparation. In indigo, and those which have been fully inves- 
tigated, the colouring matters are supplied to us in the arts in any quantity, and 
in a state approaching, at least, to purity; but in roots and plants, the case is 
very different, as they there constitute only a minute fraction of the whole mass, 
from which their separation is always attended by difficulties, and necessitates 
VOL. XVI. PART. IV. os 
