The Chemical Gazette 327, 1.6.1856
By Frederick Kuhlmann.
* Page 192.The author having found, as stated in the first part of this paper*, that pyroxyline, when deprived of a portion of its nitrous elements by spontaneous decomposition, acquired a capability of taking dyes quite opposite to that possessed by pyroxyline, commenced a fresh series of experiments with cotton stuffs, which before receiving the mordant had been in contact for a longer or shorter time either with nitric acid of various degrees of concentration, or with variable mixtures of nitric and sulphuric acids. The results were very remarkable. With Brazil wood, acetate of alumina gave violet-red tints upon non-azotized cotton; immersion for twenty minutes in nitric acid of 34°, followed by washing with a large quantity of water, and immersion in a weak solution of carbonate of soda before the application of the mordant, gave a far deeper and less violet-red colour than that taken by the cotton which was not prepared with acid. The result was confirmed by several successive trials. A ve sensible effect was produced, even by the immersion of the cotton for half an hour, in the same acid diluted with double its volume of water; and in this case the tenacity of the cotton was not perceptibly altered.
In the following comparative experiments -
No. 1 was cotton without any acid preparation;
No. 2, cotton kept for five minutes in a mixture of 2 vols. of nitric acid of 34° and 1 vol. of sulphuric acid of 66°;
No. 3, cotton kept for two minutes in a mixture of 1 vol. of nitric acid and 1 vol. of sulphuric acid;
No. 4, cotton kept for twenty minutes in a mixture of 1 vol. of nitric acid and 2 vols. of sulphuric acid;
No. 5, cotton kept for twenty minutes in a mixture of 1 vol. of nitric acid, 2 vols. of sulphuric acid, and ½ vol. of water.
After the acid baths, the stuffs were washed with a large quantity of water, passed into a bath of carbonate of soda, washed again, and finally passed into a mordant of acetate of alumina. The dyeing was effected with a decoction of Brazil wood.
No. 1 took a pale violet-red colour;
No. 2, a less violet-red tint, but still rather pale;
No. 3, a deeper and brighter colour;
No. 4, a much deeper poppy-red colour, very like that obtained with the decomposed pyroxyline;
No. 5, a deep red colour of extraordinary richness. Under the same circumstances, but with a stronger dye-bath, a splendid red colour was produced of such depth that it appeared brown. The same results were obtained in several repetitions of the experiments.
From this it evidently follows that a mixture of sulphuric and nitric acids furnishes colours most approaching scarlet, and that the best results are obtained with a bath consisting of 1 vol. of nitric acid of 34°, 2 vols. of sulphuric acid of 66°, and ½ vol. of water.
The author also made some comparative trials of dyeing with cochineal and orchil upon cotton. The mordant was acetate of alumina. Immersion of the cotton for twenty minutes in a bath of pure nitric acid, or a mixture of 2 vols. of nitric acid and 1 vol. of sulphuric acid, gave with cochineal a pale red tint, very like that produced without an acid bath. The same immersion in a bath of 1 vol. of nitric and 1 vol. of sulphuric acid gave a much deeper colour. A mixture of 1 vol. of nitric and 2 vols. of sulphuric acid gave a colour of at least double the intensity of the preceding.
With the last acid mixture also a pretty strong colour was obtained upon cotton with orchil.
With garancine a bath of nitric acid alone gave a yellower but not a deeper tint than upon cotton which had not been azotized. 2 vols. of nitric and 1 vol. of sulphuric acid gave a similar tint, but deeper than the preceding. Equal volumes of the acids gave a very fine brownish-red colour, like the Adrianople-red before avirage. 1 vol. of nitric and 2 vols. of sulphuric acid gave the same intensity of colour, but a shade more approaching orange. Lastly, twenty minutes' contact of the cotton with a mixture of 1 vol. of nitric acid, 2 vols. of sulphuric acid, and ½ vol. of water, gave a very bright red colour, of much greater intensity than the preceding.
All these experiments were repeated with wool, silk, feathers, and hair, previously submitted to the same treatment as the cotton, with remarkable results as regards the intensity and richness of the colours. Even with nitric acid diluted with 5 times its volume of water the effects are very distinct.
As in treatment with concentrated acids the threads or tissues, especially those of cotton or linen, are considerably altered, so that the preceding results cannot be generally applied in dyeing, the author attempted the fixation upon these tissues of different azotized matters produced by the action of concentrated nitric acid upon certain organic bodies. Picric acid, which does not attach itself to cotton with a mordant of alumina, gives very strong tints when the cotton has been nitrated. In this case the acid acts as a colouring matter, but it acts also as a mordant, especially in producing, compound colours, either by using baths of picric acid after the application of the ordinary mordants, or by mixing the acid in variable quantities with the colour in the dye-bath. The colours thus produced are very bright, but they are more applicable to dyeing upon wool and silk, as upon cotton the picric acid reacts in time upon the colouring matter, usually causing it to become yellow.
The author considers that from these experiments it follows, that the chemical composition of the bodies to be dyed has the greatest influence upon the fixation of colour, that dyeing is a true chemical combination, and that the effects due to capillarity, and the peculiar structure of the material are but secondary. These theoretical points will be treated in the third part of his memoir.
— Comptes Rendus, April 21, 1856, p. 711.
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