ON COLOURING MATTERS. 69 
of madder seems to be due. I have described its method of preparation and 
"properties in my last report. I may state, in addition to what I there-said, 
that rubian seems to be a nitrogenous body, since, on treating it with boiling 
caustic alkali, ammonia is evolved. This fact and the bitter taste seem to 
indicate that the medical ‘properties of madder, if indeed it possesses any, 
_ reside in this substance. 
If a solution of rubian in water be evaporated in contact with the air and 
_ with the assistance of heat, it deposits a dark brown substance, which sinks 
to the bottom in resinous drops, so that on treating the residue after evapo- 
ration with water, it is not completely re-dissolved ; and if the filtered liquid 
be again evaporated as before, a fresh quantity of the dark brown substance 
is formed, just as in the case of extractive matter. This dark brown sub- 
_ stance melts into drops in boiling water, but when cold it is brittle. It dis- 
solves in alkalies with a dark red colour, and is re-precipitated by acids in 
yellow flocks ; indeed it bears in all respects a great resemblance to the 
_ body which I have called alpha-resin. Nevertheless it seems to consist of 
more than one substance ; for if it be heated in a glass tube over a lamp, an 
abundant sublimate, consisting of shinmg yellow crystals, is obtained in the 
"upper part of the tube: these crystals very much resemble rubiacin. If it 
be treated with a boiling solution of perchloride or pernitrate of iron, the 
liquid becomes reddish brown, and gives after filtration a yellow precipitate 
| with muriatic acid, which is a proof of its containing either alpha-resin or 
_ rubiacin, or both. Hence it becomes very probable that rubiacin, the alpha- 
-Tesin, and perhaps also the beta-resin, are formed from rubian by the action 
_of the oxygen of the air. It becomes still more probable when we consider 
the following facts :—If an infusion of madder with cold water be allowed to 
_ stand in contact with the air, it will be found that after some hours the liquid 
ls filled with a number of long hair-like crystals, which are, as I have shown 
on a previous occasion*, rubiacin, generally mixed with a substance having 
all the properties of beta-resin. I have had one specimen of madder which 
gave such quantities of rubiacin on allowing the infusion to stand, that it 
collected on the surface of the liquor as a bright yellow scum, and by cry- 
allizing it from alcohol it was obtained almost in a state of purity. Now as 
biacin is insoluble in cold water, it must in this case either have been 
rmed from some substance contained in the infusion by the action of the 
air, or else it was at first held in solution by some other substance, such as 
alkali or alkaline earth from which it gradually became separated, as by 
e formation of some acid in the liquid. | incline to the former supposition, 
ad think it probable that it is the rubian which by its oxidation gives rise to 
> rubiacin. 
Xanthin.—This substance, the method of preparing which from a decoc- 
tion of madder after the separation of the colouring matters, &c. by acid, I 
e described above, is of course not a pure substance, since after ignition 
eaves a considerable quantity of fixed residue: it is also probable that it 
tains a small quantity of sugar, as I stated before. Nevertheless it pro- 
es reactions of a peculiar kind, which cannot be attributed to sugar, gum, 
any similar substance, and can only be due to a peculiar body which exists 
ly in madder. It has the following properties :—When prepared as above 
cribed, it is a thick, viscid, yellow or brownish-yellow syrup, resembling 
honey in colour and consistency, which cannot be rendered dry even by ex- 
posing it to a heat at which it begins to be decomposed. When exposed to 
the air, it becomes more liquid on account of its attracting moisture. When 
_ * See the Report of the British Association for the Advancement of Science for 1846. 
