Theoretical and Practical Investigation on the Fixation of Colours in Dyeing. (Part I.)

The Chemical Gazette 15.5.1856

By F. Kuhlmann.

It was generally supposed by those chemists who first occupied them selves with the complicated phaenomena of the art of dyeing, that azotized materials possess the greatest aptitude for the reception of dyes. In support of this, they instanced the greater ease with which silk and wool were dyed in comparison with cotton and linen. In the red dyeing of Adrianople, it was considered that the employment of baths of sheep's dung must give a sort of animalization to the cotton, and baths of cow-dung might be considered by dyers as producing a similar result. These notions, as regards cow-dung, have been abandoned by chemists, especially as several saline substances, particularly silicate of soda, have been substituted for it as a means of fixing the mordants.

M. Chevreul has shown that the more or less easy fixation of colours upon tissues depends sometimes upon the nature of the latter, and sometimes upon that of the colouring matter itself. The author has tried whether cotton modified by combination with the elements of nitric acid, or by transformation into pyroxyline, would acquire a peculiar disposition for absorbing colouring matters. He carefully prepared a quantity of pyroxyline with cotton and linen tissues, and also with cotton-wool, operating by Meynier's process with a mixture of monohydrated nitric acid and concentrated sulphuric acid. The pyroxyline was washed several times with a large quantity of water, soaked for some time in a solution of crystallized carbonate of soda, and washed again. The pyroxylized tissues were prepared for dyeing by the following treatment: - They were soaked for twenty-four hours in cold water, pressed and rinsed, then soaked in boiling water, and after a fresh washing they were half-dried and calendered for printing.

Various mordants were printed simultaneously upon pyroxylized linen and cotton tissues, and upon portions of the same in their natural state, the latter having been completely freed from foreign matters by boiling for three hours in a weak solution of carbonate of soda, then washed and treated with a bath slightly acidulated with sulphuric acid, and after being washed again and half-dried, calendered to prepare them for printing.

The azotized and non-azotized tissues were printed at the same time with the following mordants: —
Black
Pyrolignite of iron of 7° Baumé.
Thickened with starch.

Puce
2 parts of pyrolignite of iron of 10°.
1 part of pyrolignite of alumina of 8°.
Thickened with starch.

Red.
Pyrolignite of alumina of 8°.
Thickened with soluble starch.

Violet.
Pyrolignite of iron of 1°.
Thickened with soluble starch.

Lilac.
Pyrolignite of iron of ½°.
Thickened with soluble starch.

Brown.
Decoction of catechu with acetic acid.
A little nitrate of copper.

After impression, the tissues were suspended for six days in the cold, and one day in the hot oxidizing chamber. They were freed from gum in a bath of cow-dung and chalk of 158°F. for ten minutes, well cleaned, treated a second time in the same bath at the same temperature, cleaned and rinsed. The dyeing was effected with garancine in a bath of river-water slightly acidulated, commencing with a temperature of 95° F., and rising gradually in three hours to 185° F.; lastly, the tissues were pressed, rinsed, and dried. The dyed samples were halved, and one-half of each bleached with chloride of lime.

These operations proved the following facts: — All the azotized tissues remained excessively pale compared with the non-azotized ones, notwithstanding the superabundance of the colouring matter. The azotized tissue, although it rejects the mordants, appears to possess the power of combining, without their aid, with a portion of the colouring matter of madder, to judge from the yellowish tint which remains even after the treatment with chloride of lime.

To ascertain whether these results were due to exceptional causes, especially to a portion of acid which might have escaped the washings, the author repeated his experiments, soaking the azotized tissues for twenty-four hours in a weak tepid bath of crystallized carbonate of soda, rinsing them, and washing them repeatedly. They were then calendered, moistened, and printed after drying. After immersion in the mordants, they were suspended in the fixing chamber for eight days. They were freed from gum, and dried in the same way as in the preceding experiment, when exactly the same results were obtained.

Other pieces of cotton, and one of linen, were heated with a hot-bath of pyrolignite of iron, and then passed into a bath of nut-galls. The azotized tissues acquired a very pale tint compared with those in their natural state.

Dyeing with prussian blue was then tried upon cotton-wool. As in the black-dyeing with gall-nuts, the pyroxylized cotton only acquired a very pale tint compared with that in the natural state. The same results were obtained in a series of experiments with cotton wool, in which Brazil-wood was substituted for garancine.

M. Béchamp's recent experiments having shown the possibility of reducing pyroxylized cotton to its original state, the author wished to ascertain whether in this case it also regained its capacity for dyeing; he found that pyroxyline, treated by Béchamp's process, recovered its property of receiving colours.

The author had retained a considerable quantity of pyroxylized cotton tissues. These were rolled up tightly, and kept in a wide mouthed bottle closed with a cork. In about two months he observed that the bottle was filled with nitrous vapours, and that the cork, which was corroded by nitric acid, had been raised to give passage to the reddish vapours. The author was unable to ascertain the cause of this spontaneous decomposition, for some pyroxylized cotton which had been dyed and preserved for the same period had undergone no alteration. He washed the decomposed pyroxyline, but its texture was greatly changed, and tore with a slight touch, and its inflammability was considerably diminished.

The results of its analysis, as confirmed by M. Wurtz, were as follows:-
The substance was dried in vacuo at 212° and 230°F.
C 31.25
H 4.08
N 7.88

The analyses of gun-cotton give—

C H N

	Demonte and Menard.	Béchamp.
28.5	28.5	27.9
3.5	3.5	3.5
11.6	10.5	11.1

The comparison of these results shows that pyroxylized cotton after this spontaneous decomposition contains two-thirds less nitric acid than unaltered gun-cotton.

This partially denitrified pyroxyline was dyed with garancine and Brasil wood after mordanting with acetate of alumina, when the author was astonished to find, not only that it no longer rejected the colouring matter like pyroxylized cotton, but that it furnished infinitely stronger and brighter colours than non-azotized cotton treated in the same way. Thus with Brazil wood and a mordant of acetate of alumina a tint approaching scarlet was obtained, and this induced the author at once to attempt the production of a nitrated cotton with the same power of fixing colours possessed by that which he had obtained by accident. After ascertaining unmistakeably that the nitrous elements retained in this were in chemical combination with the cellulose, he soon perceived that these elements had not entered into such a stable state of combination, in the presence of salts of protoxide of iron, as that in which they exist in pyroxyline.

Decomposed pyroxyline and ordinary pyroxyline were exposed to a gentle heat in a bath of protosulphate of iron. In a very short time the altered pyroxyline acquired a chamois-yellow colour, whilst the pyroxyline took up much less oxide of iron than ordinary cotton under the same circumstances. The same differences of colour were reproduced when the oxide of iron was converted into prussian blue by a slightly acidulated bath of ferrocyanide of potassium. Thus pyroxyline, by losing a portion of its nitrous elements, not only loses its resistance to the absorption of mordants and colours, but actually becomes far more capable of becoming charged with these bodies than non-azotized cotton.

— Comptes Rendus, April 14, 1856, p. 673.