ON THE COLOURING MATTERS OF MADDER. 25 
tions of madder, except so far as to mention that Robiquet discovered in it 
a erystallized volatile colouring matter, which he called Alizarin, and that 
_ Runge described five colouring matters which he obtained from it, viz. madder 
_ purple, madder red, madder orange, madder yellow and madder brown. I 
may here state as one result of my investigation, that I agree with Runge in 
thinking that there is more than one colouring matter in madder, though [ 
am of opinion that the substances which he enumerates and describes are 
not pure. Before however entering on this part of the subject, I shall first 
give the results at which I have arrived in regard to alizarin. Alizarin is 
doubtless the most interesting and the most definite in its nature of all the 
substances contained in madder. It also presents itself the most easily to 
the observer even on the most superficial examination. If we heat madder 
spread out in a thin layer on a metal plate without carrying the heat far 
enough to char the woody parts of the root, we shall in the course of a few 
hours find its surface covered with small red or orange-coloured crystals, 
which consist of alizarin. In the same way any extract of madder, whether 
with water, alcohol or alkalies, evaporated to dryness and gently heated, gives 
a crystalline sublimate of alizarin, which is variously coloured from a light 
yellow to a dark red or brown. Now one of the first points to be ascertained 
__ in regard to this body was whether it exists as such in the root, or whether 
_ it is formed by the process of sublimation. Robiquet, the discoverer, states 
that it pre-existsin the plant. He considered alizarin as the colouring prin- 
ciple of madder, and merely subjected it to sublimation for the purpose of 
purifying it. But his investigation presents us with no convincing proof of 
_ this opinion, for the extract of madder with water, alcohol, &c., from which 
he prepares his alizarin by sublimation, shows no trace of anything crystalline; 
and many chemists have asserted in consequence that it is a product of de- 
' composition, being formed by the action of heat in the same way as pyrogallic, 
_ pyrotartaric acid, and many other bodies. I have however no hesitation 
| j in affirming that it exists in the plant as such, having in more than one way 
| Obtained it in a crystallized state without the intervention of heat. If we 
| make an extract of madder with cold water, we obtain a brown fluid which 
By produces no reaction on test paper. After being exposed however to the 
j ; action of the atmosphere for some hours, it acquires a distinctly acid reaction ; 
_ and if it be now examined carefully, there will be found floating about in it 
| a number of long hair-like shining crystals: these crystals are alizarin. If 
_ the fluid be still further exposed to the influence of the*atmosphere, a yellow 
Tisha substance begins to separate, which I shall mention afterwards. 
a 
_ This is succeeded by a gelatinous substance, and after some days a complete 
_ state of putrefaction ensues. It seems as if the alizarin in madder, or at all 
| events that part which dissolves in the water, exists in combination with lime. 
_ On exposure to the atmosphere, there is formed, from some constituent 
| of the root dissolved in the fluid through the instrumentality of the oxygen, 
| some acid, which seizes hold of the lime in the solution and separates the 
_ bodies which are combined with the lime. Now the alizarin, being a body 
_ of very slightly acid properties, is separated first, and the other substances 
- follow in succession. The fresher the madder is, the purer will be the ali- 
zarin, which separates on exposure to the atmosphere ; in some instances it 
orms on the surtace of the fluid a thick light yellow scum; but in most cases 
is mixed with brown or red substances, from which it is separated with 
difficulty. It is therefore most advisable to separate the crystals which are 
_ deposited after twelve hours’ standing, by filtration. These crystals are then 
| washed from the filter and boiled with very dilute nitric acid until they have 
| become of a bright yellow colour. They are then dissolved in boiling alcohol, 
