Dissolving Aniline Colors.

Scientific American 16, 18.4.1868

For the application of most of the aniline colors, more especially blues and violets, consumers are obliged to make use of special solvents either to prepare them for the dyebath or for printing. The solvents mostly employed are alcohol, wood spirit, and acetic acid. These solvents, seeing the quantity one is obliged to use (from two to five gallons per pound of color), are very costly, and the best means ought to be used either to diminish the quantity employed or dispense with them altogether. Many ways have been proposed. The first consists in modifying chemically the colors, especially blues and violets, by the action of concentrated sulphuric acid or the action of alkali.

The action of alkalies has given birth to the isolation of the bases of violets and blues of aniline and the formation of soluble salts by the saturation of this base with an acid.

The action of concentrated sulphuric acid has resulted in the following processes:

Nicholson heats one part of blue or violet of aniline with four parts of sulphuric acid 66° Baumé to 230° Fah., and keeps it at that temperature till the color is entirely soluble in water; the time is generally about 45 minutes.

C'avel pours (a little at a time) [-] fuming acid upon the colors, stirring all the time. After the repose of half an hour the mixture is run carefully into water saturated by an alkali which precipitates the color completely soluble in water.

M. Monet, of Lyons, mixes one part blue of aniline with one part sulphate of aniline; he takes one part of this mixture or one part of violet insoluble in water, and adds it to six parts of sulphuric acid 66°, heats gradually to 160° Centigrade, takes out the fire, and adds alkali till an alkaline reaction is shown, and the color precipitates. After washing one part of this color is soluble in 200 parts water.

The second means consists in replacing alcohol by vegetable emulsions, or by solutions emulsive of special products much less costly than alcohol.

These means have originated the processes of M. Gaulbier de Clanbry and of MM. Lailler and Dumesnil, of Rouen. The process of M. Gaulbier de Clanbry was patented in England and France in 1864, and according to his patent a large number of substances give to water the property of dissolving the colors which to that time could only be dissolved by alcohol or substances as inconvenient. His invention consists in the substitution for the alcohol and other solvents hitherto employed for dissolving the coloring matters obtained from aniline which are insoluble in water, such substances or any substances which shall possess the property of forming a mucilagenous, gelatinous, or sopanaceous solution when mixed with water, or of thickening water so as to render it mucilagenous, gelatinous, sopanaceous, or sirupy. As examples of such substances, especial mention may be made of the following: Starch or other fecula, gums, gelatine or glue, concentrated decoctions of the bark or rind known in Panama (guillaya amponairia) of the rose tribe, the soapwort of Egypt, the root of the marsh mallow, mucilage prepared from the plants or the seeds of the mallow, lily and orchis tribes, from lichens, fetus or sea wrack, and the seeds of the quince. He also mentions that other substances, though not possessing the properties of rendering water mucilaginous, gelatinous, or soponaceous or sirupy may be employed, such as glucose and glycerin. The dyeing is effected by the solutions hereinbefore described, in the same manner as when alcohol is used, but with the advantage in favor of the improved mode of preparation that the solvents do not volatilize like alcohol, and uniformity of tint is readily obtained. In the baths the fibers take up by their own action the colors which remain constantly in a state of solution, and consequently fabrics or fibrous substances dyed by this process do not lose any of their color by friction.

It is said that M. Gaulbier de Clanbry has ceded the working of this process to the house of Coly, of St. Denis. For dyeing or printing this process is probably more adapted to the violets than the blues, and has not yet acquired a very large practical importance except in the manuracture of lakes, to which it appears specially suitable. As a solvent for the aniline colors employed for this purpose gums and glue, etc., have been extensively used for some time in this country as well as in England and France. The process of MM. Lailler and Dumesnil is somewhat similar to the preceding.

The third means was patented in England and France by Mr. Leonhart, of Manchester, in 1864, and consists in reducing the colors of aniline into a state of extreme division and introducing them in this state into the dyebath without any solvent. To obtain this result the colors are completely dissolved in alcohol. The alcohol solution is run drop by drop into cold water, which is rapidly agitated. The precipitated mass is drained or filtered and well washed and the liquid is distilled to recover the alcohol, which can be used again and the paste can be employed directly in dyeing or printing.

The last plan is due to the intelligence of MM. Rangod, Pechiney and Bulard. They dissolve in cold sulphuric acid of 66° blues and violets of aniline, one part of color to six or twelve parts of acid. When all is dissolved this solution is poured into a quantity of water sufficient to determine the total precipitation, about fifteen or twenty times the weight of acid employed. The water must be well agitated and kept cool during the mixing. The precipitate, separated from the liquid and well washed, is used in the state of carmine and is applicable direct to dyeing and printing.

It is well known that the process of Rangod, Pechiney, and Bulard has given excellent results in dyeing quantities of wool, and it is truly inexplicable that the process is not yet generally applied. That the employment of alcoholic solvents, so very costly, is not abolished, is not the want of a means to arrive at the result, but only the non-application of that means.