IV. Experiments on Dying Black. By Mr. James Clegg, of Redivales, near Bury, p. 48. (1774)

The Philosophical Transactions of the Royal Society of London, For their commencement, in 1665, to the year 1800: Abridged, with notes and biographic illustrations by Charles Hutton, LL.D. F.R.S. George Shaw, M.D. F.R.S. F.L.S. Richard Pearson, M.D. F.S.A. VOL XIII From 1770 to 1776. London: Printed by and for C. And R. Baldwin, New Bridge-Street, Blackfriars. 1809Lime having been proved to increase the solvent power of water, on astringent vegetables, for medical purposes, Mr. C. was desirous of knowing if it would be equally useful in the art of dying black: to this end he made the following experiments.

Exper. 1. Four pennyweights of each of the following astringents, viz. galls, sumach, oak bark, bistort root, and logwood, were boiled during 10 minutes, in half a pint of pure river water; on mixing the decoctions with a saturated solution of martial vitriol, in the proportion of 1/3 of the solution to 2/3 of the decoction, they struck colours differently inclining to blackness, in the following order: viz. oak bark, bistort root, sumach, galls. He then boiled the same weight of all the astringents, in the same quantity of lime water, and on mixing them as above, the colours they produced were inferior to those with plain water, the astringency of the logwood, or whatever gives it the property of striking black with green vitriol, was entirely destroyed; it produced not the least blackness with any quantity of vitriol.

Exper. 2. Four pennyweights of each of the astringents above-mentioned, were tritured in plain water, and 4 others in lime water; the measures of water used were equal to those left, after boiling, in the last experiment; and, on being mixed with martial vitriol, as in the last experiment, the colours produced, by this means, were superior to those produced by boiling. Those tritured in lime-water were judged to be the deepest, which agrees with Mr. Henry's experiments; but we must again except the logwood, which gave no colour by trituration, more than by boiling in lime-water.

Exper. 3. All the above mixtures having been written with as inks, and exposed 6 months to the air; those boiled in lime-water had failed much; those tritured in lime-water, and in plain water, had faded a little; those boiled in plain water evidently preserved their colour best. On slightly rubbing the faded writings, with a fresh astringent liquor, they recovered their original blackness; by which it appears, that it was the astringent parts of those inks which had failed.

Does it not appear, by these experiments, that, though lime water tends to deepen the colour produced by some astringents and martial vitriol, it by no means adds to the duration of those colours; and as lime-water, either by trituration or coction, entirely destroys the property, in logwood, of striking black with martial vitriol, it can by no means be of service, in the black dye, where logwood is a material ingredient. Does it not also appear, that a slight boiling is preferable to trituration, for the purposes of dying, when a durable colour is wanted?

Having observed a solution of iron, in a vegetable acid, struck a deeper black, on mixture with an astringent, and produced its effects much more expeditiously, than a strong solution of martial vitriol; it occurred, that the iron, being more slightly combined with the vegetable acid than with the vitriolic, made it more easy for the astringent matter to decompound the former, and produce an ink; if this was the case, he suspected, that lime-water deepened the colour of astringent and chalybeate mixtures, not so much by its action on the astringent, as on the chalybeate, the lime uniting with the superabundant acid, and leaving the iron with so much of the acid, as is necessary for the formation of an ink, to be more easily attached by the astringent matter of the vegetable. But if this theory was well founded, it followed, from analogy, that any substance, which had a greater affinity with the vitriolic acid than iron had, would produce the same effect, in some degree, as lime. To determine this:

Exper. 4. He took 2 vessels, containing equal measures of a strong astringent liquor, composed of galls and logwood: into one vessel he put a small quantity of pearl ashes; the other remained as a standard. Pieces of linen and cotton cloth, after maceration in these liquors, were thrown together into a strong solution of copperas; they were soon after taken out, and washed in cold water; when dry, the pieces prepared in ashes were, all of them, much deeper than the others.

He made use of different kinds of pearl and pot-ashes, as well as of many kinds of astringents; the ashes had the same effect, whatever astringent was made use of, and the strongest alkali always produced the deepest colour; and though ashes, used with an astringent, always gave a deeper black, than the same astringent without ashes, yet logwood, which without ashes gave not so deep a colour as galls with them, gave a much deeper black than galls with the same addition. There was a remarkable difference, in this case, between lime and ashes, in their effect on logwood; with lime it gave no blackness; but with ashes, it produced a deeper black than any other astringent he made use of.

Being desirous of trying the duration of colours, produced by astringents, in which different quantities of pearl-ashes had been dissolved;

Exper. 5. In 2 pints of river water, he boiled 1 oz. of logwood, during 10 minutes; he then added half an ounce of Aleppo galls, and boiled them together 10 minutes longer; the liquor having stood to cool, was decanted off, and divided into 6 equal quantities. N° 1 remained as a standard; into N° 2 he put 6 grains of fine pearl-ashes; N° 3, 12 grains; N° 4, 18 grains; N° 5, 24 grains; N° 6, 30 grains: to 6 drops of each of these liquors, he added 2 drops of a saturated solution of copperas; N° 2 and 3 struck a deep black; N° 1 and 4 black, but inferior to 2 and 3; N° 5, a brown black; N° 6, brown.

From this experiment it appears, that N°5 and 6 were spoiled by an over proportion of ashes. Before seeing experiments, wherein it had been demonstrated, that a quantity of acid enters into the composition of ink, Mr. C. imagined the alkali decompounded the copperas too suddenly, and disengaged the iron faster than the astringent matter could unite with it. But most probably the alkali neutralized too great a portion of the acid. All these writings having been now exposed 6 months to the air, in N° 5 and 6 the blackness is quite destroyed; N° 4 is somewhat faded; N° 1, 2, 3, remain nearly as they were; N° 2 and 3 being still superior to the standard.

Ei kommentteja :