MADDER DTES FROM COAL. 
63 
these chemists recognised in this a body intermediate in com- 
position to anthracene and alizarin — a body, in fact, which may 
be described as anthracene half- converted into alizarin. This 
body they renamed, in accordance with the results of the re- 
searches they had been carrying on, and called it anthraqui- 
none .* 
There being no method known by which it was likely that 
anthraquinone could be directly converted into alizarin, a 
change in which it would have to take up as much more oxygen 
as it already contains, it was acted upon with bromine and 
converted into a brominated anthraquinone. This new sub- 
stance was then heated with caustic potash, by which the 
bromine was removed, but only by having potassium oxide left 
in its place. This was just what was looked for and wanted : 
more oxygen had been carried into the composition of the body, 
and the result was a substance that only differed from alizarin 
in having two atoms of potassium instead of two additional 
atoms of hydrogen. The last stage of the process presented 
no difficulty; the potassium-alizarin had only to be heated 
with an acid in order to replace the potassium by hydrogen, 
and alizarin was obtained. 
The use of bromine being undesirable for manufacturing pur- 
poses, Perkin, the discoverer of the first coal-tar dye, deter- 
mined to try whether he could not replace its use by that of 
sulphuric acid. In this attempt he proved ultimately success- 
ful ; as, however, the steps of the process are otherwise essen- 
tially the same as those already described, it is unnecessary to 
follow them out here. 
To those familiar with the use of chemical symbols the 
information afforded by them is so great that we will here 
represent by these symbols the composition and relations of 
anthracene, anthraquinone, and alizarin : 
The identity of artificial alizarin with that obtained from 
madder having been called in question, the last-named chemist 
has compared the two bodies together, and enumerates the 
following points of identity, to show the groundlessness of these 
doubts : 
* Quinone is a substance obtained by oxidising an acid called quinic acid 
found in the Cinchonas, the coffee plant, the Paraguay-tea plant, &c. ; and as 
Graebe and Liebermann found the body obtained from anthracene to belong 
to the same class as quinone, they indicated this by the term anthra- 
quinone. 
Anthracene 
Anthraquinone . 
Alizarin 
'l4 rj -8'~ / 4* 
