Blueish Eosine.—Fluoreacine, and the necessary quantity of iodine are dissolved separately in alkaline water, and mixed. An acid is added, which, by setting free both the iodine and fluoreseine, causes them to combine. A crystalline precipitate is deposited, soluble in dilute alkali, and forming the tetra-iod-fluoreacine salt of sodium or potassium. It gives a blueish scarlet eosine, soluble in alcohol. Alcoholized derivatives are obtained by heating with alcohol and sulphuric acid in a cohobator. The methylic compound is more yellowish than the ethylic. These compounds are soluble in equal parts alcohol and water. Other eosine colours are obtained, but they have not yet met with much demand. The commercial salts aro genemlly those of sodium.
Grim (1877, No. 3698 ; 1878, No. 4728), obtains colouring matters by actiog upon the diazo compounds of the nitro-phenols with certain derivatives of the phenylic series. Pieramic acid is converted into ita azo derivative, and, by treatment with carbolic acid, yields yellow or brown colouring matters ; a maroon is obtained by using reaorcine or orcine instead of carbolic acid. Beta naphthol and the azo derivative of pieramic acid gives purple ; either alpha naphthol or the sulpho napthalic acids may be used instead.
Poirrier, Rosenstiehl and Rouesin (1878, No. 4489), convert phthalamine into a sulpho conjugate body, which is afterwards nitrated into a diazo derivative ; this is united directly with phenols or amines for the production of direct colouring matters. With beta naphthol, a material is obtained which dyes wool a very intense red, aa if produced by orehel.
Alizarine; C„1160, (H0)2.—This substance is found in the dried roots of Rubiacece, and forms the principal portion of the colouring matter of the madder plant (see Dye Stuffs). The very large consumption of madder in this country made the artificial production of the dye a matter of importance, hence England has taken the lead in developing the production of the colour from coal-tar. The source of artificial alizarine is anthracene, a product from which many other colours are probably destined to be derived. The only firm engaged in the manufacture in this country is that of Burt, Boulton, and Heywood, Silvertown. The anthracene is first converted into di-brom anthraquinone, di-aulpho-anthraquinonic acid, or di-nitro-anthroquinone (q.v.), which on fusion with potash, maintained until the mass assumes a fine violet colour, yields a melt from which the colouring matter is dissolved out by water ; tbis solution, treated with an acid, deposits alizarine as a yellow precipitate.
The fusion with alkali is the most important step in the manufacture. The addition of water, the temperature, and the duration of melting, are of great moment. Too much watcr and too little heating will lead to the formation of hydro-products, or only oxyanthraquinone ; too great a heat burns the melt, and yields a dirty-green paste, which dyes greyish shades. If heated for too long or too short a time, a part of the aulpho-aalt is reduced to anthraquinone, which cannot be easily separated from the alizarine, on account of the difficulty of filtering the alkaline solutions. The purity of the tones depends on the quality of the alizarine ; if a fine or blue alizarine is required, it is beat to work on the " silver salt," which is the mono-sulph-anthraquinonate of soda. To detect whether thorough conversion into alizariue has taken place, a sample of the melt is dissolved in water, neutralized, and filtered ; the filtrate is shaken up with ether, which dissolves the alizarine and isopurpurine, whilst the aulph-anthraquinonic acid is retained by the water, and can be detected by the blue colour it gives with potash. Au aqueoua solution of the melt is heated with caustic lime, boiled, and filtered ; if the filtrate is orange, and deposits yellow flocks on the addition of an acid, Oxyanthraquinone and anthraflavie acid are present. This will not only guide a manufacturer in its production, but forma a most useful test for its commercial value.
One part of dibrom-anthraquinone ia heated in an open vessel of enamelled iron or glass to 180°-200° (356°-392° F.) with 2-3 parts caustic potash, and sufficient water t,o dissolve the alkali; the heating is continued until the mess acquires a deep-blue colour ; when cool, it is dissolved in water and filtered ; from the filtrate, alizarine ia precipitated by an organic acid ; the yellow flocks are collected in a filter, and well washed with water.
Disulph-anthraquinonic acid is mixed with about twice its weight of caustic potash or soda, and heated at 180°-210° (356°-410° F.) till its aqueous solution gives a copious yellow precipitate on addition of hydrochloric acid. It is now dissolved in water, acidulated with sulphuric or other acid, to precipitate the colouring matter, which is filtered off, and washed with slightly acid water.