MADDER, COLOURING MATTERS OF. The root of the madder plant [Rums, tineterum, in Nay. Haar. Dry is so extensively used fur the preparation of all shades of purple, red, brown, and even black dyes, that in importance to the calico-printer and others, it is second to no other dye-stuff, except perhaps indigo.
Madder grows in the south of Europe, many parte of the Levant, and is largely cultivated in I loliand. It does not contain the colouring matter ready formed, nor does the substance from which the colour is derived reside indiscriminately in all parts of the plant. It is indeed only the ligneous or woody portion of the long fibrous roots of the rubia that are valuable, and hence the various operations that are performed upon them before being sent into commerce. These pre paratory processes consist in, first, carefully drying the roots in a stove, then thrashing with a flail, winnowing and sifting away the dust or dried cellular matter, and finally, again drying, and, in nearly all cases, powdering the resulting fibres.
The ground madder thus prepared is called in France garance, but occasionally it is sent out in the entire state, especially from Turkey and the Levant, and is then called lizari or altxari (from gIeCdpi, the modern Greek name for madder).
Madder thus prepared has a reddish appearance, and contains three distinct colouring principles, namely : 1. Alizarin ; 2. Purpurin ; and 3. Rubiacin. Of these, alizarin is the one of greatest importance.
Madder also contains, 4. Cldorogenin—a green, pulverulent species of extractive matter ; 5. Erythrozym, a ferment ; and 6. Rubian, a body of deep yellow colour, not, however, a colouring principle in the practical sense of the term, but which, by the action of ferments, acids, or alkalies, yields up large quantities of alizarin.
I. Alizarin Lizaric acid. This substance, though chiefly resulting from the decomposition of rubian during the dyeing operations, has nevertheless been shown by Schunk to exist ready formed in dried madder, and has probably been produced from the rubian originally in the plant by the action of a ferment in the drying operations.
Alizarin was first discovered by Robiquet and Colin. It is identical with Runge's Madder red. It may be extracted directly from the root, but is best obtained from garancin, a substance prepared by acting upon powdered madder, with strong hot sulphuric acid, by which the earthy matter and a large quantity of valueless tissue is rendered soluble, and is removed by well washing the residue with water. The dried, insoluble portion constitutes the garancin ; it is very largely used in print works, and it is from this that alizarin is moat conveniently prepared. The garancin is boiled for some time with a quantity of water, and the colouring matters precipitated from the resulting liquor by sulphuric acid. The precipitate well washed with cold water, dried, and submitted to sublimation, yields beautiful orange coloured needles of alizarin. An impure alizarin was described by Robiquet and Colin, under the name of eolorin.
Alizarin is tasteless and inodoroua, neutral to test paper, almost insoluble in cold water, more so in hot water, and freely taken up by alcohol or ether. The alkalies dissolve it, forming a beautiful purple solution, but acids reprecipitate it unchanged. It terms a splendid red lake with alumina, and purple ones with lime, baryta, and oxide of iron. Alizarin is converted into phthalic acid (alizaric acid, by ebul lition with dilute nitric acid, and since chloroxynaplithalic acid, a body prepared from naphthalin, also yields phthalic acid under the same cir cumstances, it has been thought, that chloroxynaphthalie acid is simply alizarin with an atom of hydrogen replaced by one of chlorine. Schunk, however, does not think this to be the case, nor has Strecker himself, who was the first to throw out the hint, been able to replace the chlorine in chloroxynaphthalic acid by hydrogen and thus convert it into alizarin. Were this accomplished, naphthalin would no longer he a waste product as it now Is, but become of great value and importance.