Murexide as a Coloring Matter for Wool.

Scientific American 4, 7.10.1854

- The following article form the Bulletin de la Societic Industrielle de Mulhouse, will be read with great interest by all our chemists, in woolen cloths, carpet, shawl, and de laine manufactories:

"The beautiful researches of Liebig and Wohler upon uric acid and its derivates made us acquainted with a peculiar substance, to which they gave the name of allonxan. This body is obtained by adding very gradually 1 part of uric acid to 4 parts of nitric acid, of a specific gravity of from 1.45 to 1.5. The uric acid is dissolved with evolution of nitrogen and carbonic acid, accompanied by a considerable rise of temperature, which must be prevented as much as possible; on coolong, the mass becomes nearly solid, from the deposition of white granular crystals of alloxan. If these cyrstals be drained and dissolved in a very small quantity of water, and exposed to spontaneous evaporation in a moderately warm room, large, brilliant, colorless crystals, in the form of short right rhombic prisms, will be obtained. Alloxan is remarkable for the facility with which it undergoes changes when treated with different substances, and for the number of curious compounds thereby produced. Thus if sulhuretted hydrogen gas be passed through a solution of it, sulphur is precipitated and a new body formed, to which the name of alloxantine has been given; or if its solution be slightly acidulated and a slip of zinc placed in it, the same body will be produced under the influence of the nascent hydrogen evolved during the dissolution of the zinc. Alloxantine being sparingly soluble in cold water, readily separates in crystals, which may be obtained pure by solution in hot water, for, unlike alloxan, it is not decomposed by continued boiling. If 4 parts of alloxantine and 7 of alloxan be dissolved in 240 parts of boiling water, and 80 parts of carbonate of ammonia be added, a very peculiar body will be formed, which will crystallize on the liquor cooling. These crystals are of a beautiful garnet-red color by transmitted light, and have a beautiful iridescent green by reflected light. To this body the name murexide was given, from the Murex or shell-fish, from which it was supposed the Tyrian purple was formerly procured. Previous however to the experiments of Liebig and Wohler, Dr. Prout had described the same substance under the name of purpurate of ammonia, but obtained in a somewhat different way. So readily is this body formed, that a solution of alloxan will stain the skin purple in consequence of its production. This fact led its second discoverers to imagine that, like the Tyrian purple, it might be employed as a dye-stuff. The difficulty however of obtaining it, and of fixing it upon the fabric when formed, prevented for that time the idea from proving fertile.

Some time since, however, Dr. Sacc turned his attention to the subject, and led by the fact above mentioned, that a solution of alloxan stained the skin, came to the conclusion, that by impregnating a piece of woolen cloth with that substance, he might be able to produce the murexide directly in the tissue. He tried the experiment, and succeeded in dyeing a piece of cloth of an amaranthus tint, far more beautiful than that produced by cochnieal. He communicated the results of his first experiments, still incomplete, to M. Alvert Schlumberger, who has succeeded, by modifying and completing the experiments of Dr. Sacc, in rendering the process, merely indicated by the latter, perfectly practicable.

His process is simple enough. He prepares a solution of alloxan, formed of 30 grms. of allonxan to each litre of water, and soaks the tissue to be dyed in it, the excess of liquid being then squeezed out int he ordinary way, or by pressure between rollers. The cloth is then dried at a gentle temperature, and after an ageing of twenty-four hours the color is brought out by passing the cloth over a roller heated to 212°F. For this purpose the drying machines composed of several drums would answer perfectly, the cloth being successively passed over each, the greatest care being taken to avoid the folds; woolen yarn and wool should be put in a stove heated by steam. According as the heat is communicated to the cloth, a magnificent purple tint, far more beautiful than anything hitherto produced by the ammoniaval preparation of cochineal, or by red dye-woods, makes its appearance as if by magic. The intensity varies according to the stregth of the solution of alloxan which has been employed. It is only necessary to wash the cloth in cold water to give to the shade its full brilliancy.

M. Sacc found that the finest and most vivid shades could only be communicated to the tissues mordanted wit hsalts of peroxyd of tin, and M. Schlumberger has confirmed this observation. Cloth not mordanted did not give very satisfactory results, even after a prolonged exposure to warm and damp air. He obtained the most satisfactory results by soaking the cloth in a solution composed of equal parts of perchloride of tin and oxalic acid, of a specific gravity of 1.006. In this solution, at a temperature of about 100°F., the cloth is to be allowed to remain for an hour, then rinsed and dried, and is then fit to be treated with alloxan. If stronger solutions of the mordant be employed, there is a considerable loss of coloring material, and a detorioration of the shade. - This may be attributed to the presence of too great an excess of stannic acid, which from its opacity may mask the murexide, or by its acid re-action may decompose it. This is especially the case if chloride of tin be employed instead of stannate of soda. Experience has shown that fabrics freshly mordanted give better results than those which have been mordanted for some time; the depreciation in purity and brilliancy of tint in the latter may even amount to 20 or 30 per cent.

Murexide, as we have already remarkded, being produced by the action of heat and ammonia, it occurred to M. Daniel Dollfus, and the other members of the committee for the chemical arts, appointed by the Societe Industrielle of Mulhouse, to report upon the memoirs of M. Schlumberger, to try the effect of exposing a piece of cloth, treated with alloxan, to the vapors of ammonia. The result confirmed their anticipations, for the color was immediately produced without the necessity of ageing the cloth after its impregnatin with the alloxan. - There can therefore be no doubt that the best results will be obtained in future by the employment of ammoniacal vaports, for, besides the saving of time, there will also be a saving of alloxan. This substance is very liable to decompose, especially in the presence of even minute traces of reducing agents, such as protochloride of tin or sulphurous acid; traces of the latter substance always remain in the cloth after the operation of bleaching, not matter how well washed it may be, and would be quite sufficient to prevent the formation of the murexide.

As yet all the attempts that have been made to communicate the murexide-purple to cotton or silk have failed, that substance having an affinity apparrently only for wool, to which it gives a very permanent and durable dye. Sunlight, so destructive to other purples, appears to have but little action upon that of the murexide; a piece of cloth dyed of a rose color had its tint scarcely altered by evposure to the full action of the strongest sunshine during two days, and the color was only fully discharged by an exposure of more than two months. - Boiling water and steam completely destroy the color produced upon cloth mordanted with salts of tin; the decoloration commences in boiling water at a temperature of about 158° F., and augments with the increase of temperature. - This destruction of the dye is caused by the action of the mordant, for cloth dyed without the use of a mordant not only supports to a certain extent the action of boiling water, but even acquires a uniform, and perhaps a more beautiful and deeper tint than that given by prepared woolen fabrics. Further experience ma yshow that hot water and the application of ammonia alone may be advantageouly substituted for the mordanting and the passage over heated cylinders.

(To be concluded next week.)

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