134 
properties. The process itself", as described by its disco- 
verers, Grabe and Liebermann, seems exceedingly simple, 
and consists in the conversion of the hydrocarbon anthra- 
cene C U H 10 by the action successively of an oxidising agent, 
of bromine or sulphuric acid and of caustic alkali into aliza- 
rine C 14 H 8 0 4 . Nevertheless, the product obtained on a large 
scale for the use of dyers and printers by this process is very 
far from being pure alizarine, so far indeed that some per- 
sons are inclined to doubt its perfect identity with the 
natural substance. Its solution in caustic alkali, for instance, 
has not the fine violet colour of a solution of pure alizarine, 
but is more or less purple or even red, and it differs in other 
respects. Now, though I have never entertained much 
doubt as regards their identity in the main, it might, I fan- 
cied, be interesting to ascertain whether the differences 
observed between the natural and artificial products were 
due to impurities accompanying the latter or not, for though 
these impurities, if present, might not cause any injury or 
inconvenience during the dyeing process, they might pos- 
sibly be formed at the expense and take the place of aliza- 
rine, and thus be a source of loss to the manufacturer. 
Now a few simple experiments are sufficient to prove that 
artificial alizarine as ordinarily prepared is always accom- 
panied by other substances, some of which are coloured 
while others are colourless or nearly so. My object on the 
present occasion is to describe one of these substances and 
to point out the relation in which it stands to alizarine. 
My attention was first directed to this part of the subject 
by the results of some experiments made on a small scale to 
obtain alizarine from anthracene according to the directions 
of Grabe and Liebermann. I was surprised to find that in 
spite of all the precautions taken I always obtained besides 
alizarine a notable quantity of another body also crystalline, 
but dissolving in alkalies with a yellow colour. This body 
bore so strong a resemblance in some of its properties to 
