The extensive Magenta series includes the rosaniline group, represented by the aniline vio lets and methyl violet, and the pararosaniline group, represented by spirit blue, opal blue, etc. Among the aurines are benzaunne, an intense red, and eriochrome cyanine R, giving a brick red on wool. This may be changed to a violet blue by after-chroming.
Xanthene Dyestuffs.— Xanthene upon oxida tion yields the ketone xanthone, and this is con vertible into xanthhydrol by reducing agents. To obtain dyestuffs it is necessary to introduce auxochromes in the p-position to the carbon atom of the methane residue in xanthene, and to oxidize the leuco-bases thus produced. To this group belong the Pyronines— dyes containing the pyrone aring.° They dye silk and tannin mordanted cotton shades of pink. The phtha leins, represented by the eosines and erythro sines and rhodatnines, including the violamines, anisolines and succineins, belong in this group.
Acridine Dyestuff s.— Closely similar to xan thene is hydroacridine, the oxygen atom in the former being replaced in the latter by the div alent NH group. Upon being oxidized, hy droacridine yields acridine, a basic yellow sub stance which forms fluorescent solutions. Two forms of acridine are recognized: the symmetri cal, springing from combinations with amines, and the asymmetrical, friim combinations with diamines. The commercial dyes of this class are generally hydrochlorides. The principal dyes in this class are acridine yellow, dyeing tanned cotton a shade of yellow; benzoflavine, which gives yellov- shades on wool, silk and tanned cotton; and chrysaniline, a component of the dye phosphine, used in dyeing leather and printing cotton goods.
A n thracene Dyestuff s.— Oxidized with chromic acid, anthracene yields the important chromogen anthraquinone. From this, dyestuffs are obtained by introducing OH, NH., NR. etc., groups in suitable positions. The anthra quinone dyestuffs are classified as (1) oxyan thraquinones; (2) amidoanthraquinones; and (3) those which contain also another chromo gen besides anthraquinone.
The oxyanthraquinones dis'solve in alkalis to form violet or blue solutions. Their value as dyes depends on the fact that they form in soluble lakes with metallic hydroxides. The
most important members of the group are alizarin and purpurin, both of which are formed naturally in the root of the madder plant. Alizarin gives shades of bluish-red to violet and brown, with different mordants. Purpurin gives shades of scarlet on an alumina mordant. Anthracene blue is another important dye in this group; with chrome-mordanted material it gives a shade of blue.
The amidoanthraquinone and hydroxyamido anthraquinone dyestuffs produce very bright shades which are fast as to light. The most important are those which contain one or two NHR groups, where R represents a sulphonated aromatic nucleus. In the amido-group are alizarin cyanine green, anthraquinone violet, and alizarin astrol: in the hydroxyamido group, alizarin saphirol, alizarin celestol and alizarin irisol.
Among the dyestuffs arising from the com bination of other chromogens with anthra quinone, characteristic examples are alizarin blue, alizarin green S and alizarin indigo blue.
An important group of dyes of the anthra cene class are the so-called anthraquinone vat dyestuffs. They are insoluble in water, but give soluble products on reductions and have a decided affinity for textile fibres. These vat dyes are complex compounds of high molecular weight, containing nitrogen, sulphur and other groups in addition to the ketone groups of an thraquinone. They are classified as indan threnes (a title now used for all the anthra quinone vat dyes), in shades of blue, gray and maroon; flavanthrenes, or indanthrene yellow, also orange and scarlet; benzanthrones, includ ing cyanthrene and violanthrene indanthrene violet and indanthrene green; the anthraqui noneimides, indanthrene red G and indanthrene bordeaux B; and the acylamidoanthraquinones. comprising the extensive series of the algol dyes—in shades of yellow, red, blue and violet. These vat dyes are used almost exclusively for the dyeing of cotton, but may be employed also for wool which has been treated with formalde hyde.
Quinone-Imide Dyestuff s.— This class in cludes the indamines and indophenols derived from and the oxazines, thiazincs and aztnes derived from ortho-quinone.