however, we go one step further back and examine the fresh root 
of Rubia tinctorum, that is, as soon as it is drawn from the 
On slicing the root it is seen to be of a light carroty colour, and 
an almost colourless liquid can be squeezed out of it, but this is 
entirely free from the colouring matters of madder. 
_ roots, however, be kept if only for a short time, and then they 
_ up into alizarine and into sugar. 
im z eee 
: as a i 
Sept. 18, 1873] 
obtain this latter body heat had always been used, so until the | 
elaborate experiments of Schunk it was a question whether the | 
heat did not produce a radical change in the substance, whether, | 
in a word, these two bodies were really identical. Schunk’s | 
experiments proved that they were, and consequently that this — 
beautiful colouring matter alizarine existed as such inmadder. If, | 
und, for some time we shall find no trace of alizarine there. 
Let the 
will give abundant evMence of the presence of alizarine ; if 
simply heated alizarin may be volatilised from them. It appears 
then that the whole of the tinctorial power of this root is developed 
after the death of the plant. Schunk explains this curious phe- 
nomenon as follows :—That in tne cells of the living plant there 
is a substance which he has isolated, and has named rubian; 
it is easily soluble in water and in alcohol; the solution is of a 
yellow colour, and has an intensely bitter taste ; when dry it is a 
hard, brown, gum-like body. It has none of the properties of a 
_ dye stuff, but if we take a solution of it, add some sulphuric or 
hydrochloric acid to it, and boil, a yellow flocculent substance 
will slowly separate out, and on filtering it off and washing it, 
it will be found to have the tinctorial properties of madder and 
to contain alizarine. In the liquid filtered from it there is, with 
_ the acid added, an uncrystallisable sugar, so that in this way the 
original product in the root, the rubian, has apparently been split 
To apply this reaction to what 
ae on in the root after its removal from the ground, we have to 
nd if any other substances can take the place of the boiling 
dilute acid, and Schunk has shown there exists in the root itself 
a substance which is eminently fitted to produce this splitting 
up of the rubian. He obtained this decomposing agent from 
madder simply by digesting it in cold water, and then adding alco- 
hol to the liquid ; this threw down a reddish flocculent substance, 
and if only a small portion of this be added to an aqueous solu- 
tion of rubian and allowed to stand for a few hours in a warm 
place, it was found that the rubian was gone, and in place of it 
there was a thick tenaceous jelly ; this, treated with cold water, 
gave to it no colour, no bitter taste, but much sugar. From 
the jelly, remaining insoluble, alizarine could be extracted. In 
fact, of all known substances this very one found in the madder 
itself is best suited for effecting this decomposition of the rubian, 
It appears, then, that these two bodies must exist in the root. 
The history then seems complete. The two substances are kept 
apart during the life of the plant in some way of which we know 
nothing, but as soon as it dies they begin slowly to act on one 
another, developing thus the colouring matters in madder. It 
has long been known to dyers that the amount of colouring 
matter in madder will increase on keeping it ; even for years it 
will go on improving in quality, and an experiment of Schunk’s 
shows that the ordinary madder as used by the dyer has not all 
the rubian converted into colouring matter, for on taking a 
sample of it and extracting it with cold water he got an acid 
solution devoid of dyeing properties, but on allowing this solu- 
tion to stand some time it gelatinised and then possessed dye- 
ing properties. 
Coincident with the appearance of Schunk’s first paper was 
one by Debus on the same subject. He looked upon alizarine as 
a true acid, and gave it the name of Lizaric acid, but as far 
as the composition of it was concerned the percentage which 
he obtained agreed closely with those given by Schunk. One 
other investigation concludes all that is important in the his- 
tory of alzarine as obtained from madder. This last research 
is of great interest; it was by Julius Wolff and Adolph 
Strecker, and published in 1850. They confirm the results of 
others so far that there are in the madder root two distinct 
colouring substances—this important one alizarin, and the other 
one purpurine. They prepare these colouring matters much in 
the same way that Schunk aid, and very carefully purify and 
analyse them ; the formulz which they give for them differ, how- 
ever, from Schunk’s ; for alizarine they give the formula C3,H 20, 
and for purpurine C,,Hy,O,. Further, they suggest that by the 
process of fermentation the former is converted into the latter, 
and they show that by oxidation they both yielded phthalic 
acid. Since the publication of this research, until the last 
year or two, this formula for alizarine has been generally adopted 
¥ by chemists, and in most modern books we find it given as 
‘ 
7 
= 
= 
NATURE 
Ary 
expressing the true composition of that body. It was not only 
the careful and elaborate work which they devoted to the 
subject, but also the ingenious ‘and apparently well-founded 
theory on the subject which carried conviction with it. Laurent 
had shown, not many years before, that when naphthalin, that 
beautiful white crystalline substance obtained from coal tar, 
was acted on by chlorine, and then treated with nitric acid, 
a body known as chlornaphthalic acid and haying the composi- 
tion CoyH4 ClO, was obtained, and on comparing this formula 
with the one they had obtained for alizarine, Wolff and Strecker 
at once concluded that it really was alizarine, only containing 
two atoms of chlorine in place of two of hydrogen; make this 
replacement, an operation generally easily performed, and 
from naphthalin, they had prepared alizarine. Further, this 
relationship between chlornaphthalic acid, and alizarine is borne 
out in many ways ; it, like alizarine, has the power of combining 
with different basic substances, has a yellow colour, is insoluble 
in water, melts at about the same temperature, is volatile, and 
when acted on by alkalis gives strongly coloured solutions. Taking 
then all these facts into consideration, can we wonder that these 
chemists feel convinced that they have established the composi- 
tion of alizarine, and have shown the source from which it is to 
be obtained artificially? Apparently but one very simple step 
remains to crown their work with success, that of replacing the 
chlorine by hydrogen. Melsens had only shortly before shownhow 
this substitution could easily be made in the case of choracetic 
acid by acting on it with potassium amalgam, and Kolbe had 
used the battery for the same purpose. Both these processes, and 
doubtless all others that the authors can think of, are tried upon 
the chloronaphthalic acid, but chloronaphthalic acid it remains,, 
and they are obliged to confess they are unable to make this 
substitution. Still they are strong in the belief that it is to be 
done and will be done, and conclude the account of their 
researches by pointing out the great technical advantage it will 
be to get alizarine from a worthless substance suchas naphthalin, 
One cannot help even now sympathising with these chemists in 
their not being able to confirm what they had really the strongest 
evidence for believing must prove to be a great discovery. We 
now know, however, that had they succeeded in effecting this 
substitution, or had they in any other way obtained this chloro- 
naphthalic acid without the chlorine, if I may so speak of it, 
which since their time has been done by Martius and Griess, 
alizarine would not have been obtained, but a body having a 
remarkable parallelism in properties to it would have been. This 
body, like alizarine, is of a yellowish colour, but slightly soluble in 
water, easily in alcohol and in ether, is volatile, and on oxida- 
tion yields the same products, it is, in fact, an analogous body, but 
belonging to another group. We also know that the formula 
proposed by Wolff and Strecker, and so long in use, is not the 
correct one. But little more remains to be added with regard 
to the history of alizarine as gathered from the study of 
the natural substance. Schutzenberger and Paraf suggested 
doubling Wolff and Strecker’s formula for alizarine, and Bolley 
suggested the formula C.,H);0,;, which owing to the uneven 
number of hydrogen atoms was soon rejected. If we compare 
our present knowledge of alizarine with what it was when these 
researches on the natural product were completed, it is as light- 
ness compared to darkness, and we may well ask whence has 
come this influx of knowledge? the answer I hope to show you 
is undoubtedly that it has come from the careful and accurate 
study of abstract chemistry. I know of no history in the whole 
of chemistry which more strikingly illustrates how the prosecu- 
tion of abstract science lays the foundation for great practical 
improvements, My object now, is then to show you, as 
shortly as I can, how by indirect means the composition of 
alizarine was discovered, how it has been built up artificially, and 
how it is superseding for manufacturing purposes the long-used 
natural product. 
To trace this history from its source we must go back to 
1785, when an apothecary of the name of Hofmann obtained 
the calcium salt of an acid called quinic acid from cinchona 
bark. This acid is now known to be of common occurrence 
in plants, it exists in the bilberry and in coffee, in holly, 
ivy, oak, elm, and ash leaves, and probably many others. 
Liebig also prepared the calcium salt, and was the first to 
give a complete analysis of it; the formula he gave. for it was 
C,;H2,0,s. Bauss on repeating Liebig’s experiments arriyed at 
a somewhat different conclusion, and gavejthe formula C);H 904). 
In 1835 at Liebig’s suggestion, to determine which formula was 
correct, Alexander Woskrensky, from St. Petersburg, then a 
