MADDER DYES FROM COAL. 
61 
ments, principally, it became known that cold water dissolves 
out of madder-root, besides other matters, the colouring matter 
alizarin, a yellow bitter substance now known by the name of 
rubian after that of the genus rubia, and a highly nitrogenised 
matter acting as a ferment. The brown aqueous solution thus 
obtained is at first transparent and of a sweetish bitter taste, 
but in a short time it becomes turbid and for some hours con- 
tinues to deposit an orange-coloured, flocculent powder, the liquid 
at the same time losing its bitterness. The explanation of 
these phenomena is that the yellow substance, rubian, under- 
goes fermentation by the influence of the nitrogenised and 
highly putrescible substance which is present at the same time 
in the freshly-prepared aqueous liquid. 
Higgins showed that the colouring matter alizarin already 
existing in the fresh liquid might be removed from it by suit- 
able means, so as to deprive the latter of active dyeing powers, 
and that then, by letting this stand in a warm place, fermenta- 
tion would proceed, all the bitter matter rubian disappear, and 
a fresh quantity of colouring matter be formed in the liquid. 
On the other hand, he showed that, by using boiling water to 
make the extract of the madder-root, the ferment was coa- 
gulated and deprived of its activity, the liquid remained per- 
manently bitter, and only that quantity of colouring matter 
present at the time in the root could be obtained. He also 
established that, as in the ordinary fermentation of grape- 
juice, the presence of air was non-essential to the continuance 
of the change in the infusion of madder made with cold water 
when once it had been started, there only remained to be 
made the legitimate assumption that, in accordance with De- 
caisne’s observations upon the juice within the cells of the 
plant, even the dyeing matter always found in the most 
freshly-prepared infusion of the root is derived from the same 
source, the bitter matter rubian. 
Schunck soon afterwards observed that rubian also yielded 
alizarin when treated with the mineral acids. Much of the 
madder used by the dyer is indeed first subjected to the action 
of sulphuric acid, by which it is converted into what is called 
in the arts garancin . By this treatment not only does the 
quantity of alizarin appear to be increased, but colouring and 
other matters which affect the purity of the desired tints are 
some of them removed and some so far modified as to become 
inactive. 
Alizarin is one of those dyes which require the use of 
mordants, that is, of substances serving to fix it to the fibres of 
cotton or woollen fabrics. These mordants also serve to develop 
the colours which madder (or alizarin) imparts. Thus pre- 
pared with aluminum hydrate, cloth takes a Turkey-red colour 
