ON COLOURING MATTERS. 57 
On Colouring Matters. By Lnwarp Scnuncx. 
® 
_ In the report which I had the honour of presenting last year to the British 
Association on Colouring Matters, I gave the results of my investigation of 
_ the colouring matters of madder. This investigation I have continued and 
brought to a conclusion. The subject has however proved se extensive, the 
number of questions arising in regard to this valuable and extensively-used 
_ tinetorial substance being very great, that I have been unable to examme any 
other colouring matters very minutely. 
I stated in my last report, that when finely-ground madder roots are treated 
_ with hot water, a brown liquid is obtained having a sweetish bitter taste, in 
which acids produce a dark brown precipitate. ‘This precipitate L stated to 
consist of six substances, viz. two colouring matters, two fats, pectic acid and 
_a bitter substance. ‘To these I now add a seventh: it is a dark brown sub- 
_ stance which remains behind when the other substances have been removed 
_ by means of boiling water and alcohol ; it is soluble in caustic alkalies with 
_a dark brown colour, and seems to be the substance to which the colour of 
_ the dark brown precipitate is due: I consider it to be oxidized extractive 
matter. Concerning the method of separating the other six substances con- 
_ tained in the dark brown precipitate, | have nothing to add to what I said in 
my iast report, as I have not been able to discover a shorter or better plan 
_ of separating them than that which is there described. In regard to their 
nature, properties and composition, which I have examined more minutely, 
IT shall in this report give a number of additional details ; before doing so 
however I shall make’a few observations on the subject in general. I may 
_ State, in the first place, that I have arrived at the conclusion that there is 
only one colouring matter contained in madder, viz. alizarin; the other sub- 
‘stance, which I took for a colouring matter in the first instance, and which I 
called rubiacin, I now consider to be no colouring matter at all, for reasons 
which I shall presently state. I have also reason to believe that the two sub- 
_ stances which in my first report I called fats, are not fats, but resins ; they 
are coloured resins similar to many others known to chemists. Of these two 
resins I shall call the more easily fusible one, which dissolves in a boiling 
solution of perchloride or pernitrate of iron, the alpha-resin ; the other less 
easily fusible one, which forms an insoluble compound when treated with 
_ perchloride or pernitrate of iron, the beta-resin. The method of preparing 
them is the same as that which I described in my former report. After the 
dark brown precipitate produced in a decoction of madder by acids has been 
ecessively treated with boiling water and boiling alcohol, there remains 
‘behind a dark brown substance; on treating this substance with caustic 
potash, it dissolves in great part with a dark brown colour ; on filtering there 
remains on the filter a mixture of peroxide of iron and sulphate of lime ; on 
adding a strong acid to the filtered liquid a substance in dark brown flocks is 
precipitated, which is thrown on a filter, washed and dried. This substance, 
when heated on platinum foil, burns without much flame, and leaves a con- 
siderable ash. It is easily decomposed by boiling dilute nitric acid, which 
converts it with an evolution of nitrous acid into a yellow flocculent sub- 
ance, As it is insoluble in all menstrua except the alkalies, it may be 
asked, how it can be extracted from madder by means of boiling water, in 
; which it is of itself insoluble, and whether it is not possible that it may be 
_ formed during the process of boiling by the action of the air on some sub- 
" stance contained in the extract. I think the latter supposition very probable, 
4 
‘ 
