PART II.
We entered upon the subject of indigo, which we have treated at some length in our last issue, as much in the interest of the people as of manufacturers, for we were deeply impressed with the conviction that no improvement in our manufacturing processes would confer more benefit upon the masses than imparting stability of color to the clothing of the people. When one has a deep conviction upon a subject, upon which others have equal opportunities for judging, he may be sure that he is not alone in his impressions. He is moved by one of those waves of thought which, operating simultaneously upon many minds, gives that uniformity to public opinion at which we so often wonder. We are gratified to find, from responses to our last article, that we are not alone in our conviction of the importance of reviving “true blue” dyes. The head of a mercantile house, the extent of whose clientèle in mills both of wool and cotton is hardly surpassed, has assured us that we have not overstated the reform in dyeing which we have advocated. He had long shared in our convictions. Pointing to the throng of men in the crowded street, where we were conversing, he remarked that there was hardly a man in the crowd whose clothing would not have been improved by indigo dye. “The failure to use indigo dyes,” he emphatically said, “costs the laboring people of this country millions of dollars every year. The fault is not to be charged to our own manufacturers alone; for the blue coat which I wear, and which I bought in Paris, annoys me by the crocking caused by its aniline dye.” In one very large mill of which he is director as well as selling agent, he is putting his principles in practice. All the heavy blue cloths intended for popular consumption are faithfully dyed, and each bears a stamp, “Warranted indigo dyed.” The ready-made clothing establishments which largely consume these goods have already found their advantage in purchasing them, and a similar stamp is attached to each article made from this cloth.
Some of our most celebrated cotton fabrics have won and still retain their reputation by the use of indigo dyes. The ginghams are a signal illustration. The blue check is formed by weaving cotton yarns dyed blue in the cold indigo vat with undyed yarns. These goods can be washed indefinitely without change.
Another illustration is the famous A.B.A. Amoskeag tickings, an article of such excellence that the question of the right to use trade-mark A.B.A. gave rise to the leading American case in this branch of law. [3] A prominent feature in these goods was and still is the permanence of the dye in the blue stripe, produced by the cold indigo vat. Still another illustration is the blue and white “shirting stripe” first made by Mr. Samuel Batchelder, at the Hamilton Mills, now so generally adopted for sailors’ shirts. The indigo dye enables the color to resist the roughest possible usage.
To recur to the application of indigo dyeing to wool and woollens. We have been unable, although we have written more than fifty letters of inquiry upon the subject, to learn of any peculiarity or improvements in the American processes of wool dyeing with indigo. [4] Our dyers are for the most part foreigners. For this reason, or because the art of indigo dyeing has long since reached perfection in the best establishments abroad, they rigidly pursue the old European methods. The best dyers regard the successful management of the warm fermenting vats for wool as the highest test of their art. We have already spoken of the complicity of the phenomena in fermentations. Practical dyers endow the fermenting vat with a sort of personality. “An indigo vat,” says one to us, “is more like a sick man than any thing in the world: you have to watch it as you would a sick patient, and give it physic or ferments to stir up the system and purify it.” [5] The diagnosis of a sick vat requires that sort of instinctive knowledge which experience gives to the practised physician. The impatience of our young Americans will not permit them to serve the long apprenticeship necessary to acquire the proper experience. The artisans not thoroughly trained will naturally prefer the dyes and processes introduced by modern science, which require but little skill in their application. It is a curious fact that the influence of the national government has been largely instrumental in preserving the old system of indigo dyeing. Thanks to the Quartermaster-General’s Bureau, or the man of science, General Meigs, who presides over it, indigo dyed cloths have been persistently insisted upon for the army. The late war gave a new impulse to indigo dyeing. A skilled dyer, whom we have consulted, was constantly employed in Connecticut, on a tour of professional inspection of a dozen or more different establishments making army goods. No doctor, he says, ever found in hospital practice more complications of disease than he found in the ailing vats. Among other difficulties there was a deficiency of imported woads, although the cultivation of excellent woad immediately sprung up in Connecticut. In the mean time carrot and rhubarb tops were used as substitutes for the fermenting material of the woad. Carrot-tops grown expressly for that purpose brought as high as twenty-five cents per pound. Since the war the requisitions for indigo dyed woollen goods have not relaxed, and the art is not likely to be lost.
With the real difficulties which attend the process, it is hard for indigo dyeing to sustain itself in the face of cheap substitutes of easy application, such as the Nicholson blue. It is exceedingly difficult to piece dye with indigo and preserve a uniform hue upon the cloth. Hence indigo dyes are generally given in the wool. The wool absorbing the foreign material of the dye is more difficult to work in the operations of carding and spining. In other words, a finer and costlier wool is required. A great desideratum therefore is a means of piece dyeing with indigo so as to preserve a perfect uniformity of hue throughout the piece. This, we are happy to say, has been recently successfully accomplished by one of the largest and most faithful of our cloth-making establishments. It would be premature, before the patents are secured for this invention, to explain the ingenious and expensive apparatus devised for this purpose, which constitutes in fact a battery of vats so arranged that the operation may be continuous. The experiments authorize the statement that bottom dyes of indigo, so desirable for a great variety of colors, can be applied with no other additional cost than that of the dyeing material. When this establishment, as it proposes, stamps upon the cards which designate goods, already so admirable in material and texture, “Warranted indigo dyed,” we shall regard it as an era in the American card-wool manufacture.
The old European woad vat process is that used in all our establishments. Mr. Henderson of the Washington Mills, whose experience as a practical dyer of wool is exceptionally large, informs us that he has found no work so instructive upon this process as Napier’s “Chemistry of Dyeing” (published by Henry Carey Baird, of Philadelphia, 1869). Napier’s description of the process is extracted from Dumas’s “Lectures on Dyeing.” The appreciation expressed by so competent a judge induces us to reprint Dumas’s description in an appendix to this article.
That we may give at least a general view of the whole subject, we will proceed to consider indigo in some relations not yet adverted to.
In Part I. of our notes we have treated only of the application of this substance in dyeing by means of reduction through the indigo vat. Indigo may be applied by means of reduction in the printing of fabrics, as well as in dyeing them. A true scientific arrangement would compel us next in order to consider this other application of indigo by means of reduction. But the more natural and practical order is to pursue the subject of dyeing, and to consider next the applications of the derivatives from indigo in dyeing proper.
See the case stated at length in our article on Trade-marks, Bulletin, vol. i. p. 102.
A reply by Mr. D. R. Whitney, an extensive indigo importer, to a letter of inquiry, enables us to correct some errors in our former article, under the head of “commerce in indigo.” The value of export from India in 1862–63, stated in dollars, through a typographical error, should have been pounds sterling; thus, instead of $2,126,814, read £2,126,814. It is stated in our first article that the telegrams show a decline of price of indigo in the Indian trade of from 50 to 75 per cent; “per cent” should read “rupees,” which would make a decline of from 25 to 30 per cent. The reason for the decline, as stated by Mr. Whitney, is the unusually large crop of this year. The average crop of indigo in Bengal is about 100,000 maunds. The crop of this year is 135,000 maunds, about 30 to 35 per cent above the average.
According to Mr. Whitney, the consumption of Bengal indigo in the United States was 2,458 cases of 270 lbs. to a case on an average, in 1871; and in 1872, 1,802 cases. Guatemala indigo, 3,132 serroons in 1871, and 2,578 serroons in 1872.
See notes on “sickness” of vats in Appendix.
SULPHURIC DERIVATIVES,—SAXON BLUE, &C.
The powerful action of sulphuric acid upon indigo, and the bright and lively blue color thereby produced, had been observed by chemists long ago; but no person appears to have applied this color upon cloth, until it was done about the year 1740, by Counsellor Barth, at Grossenhein, in Saxony. The vividness of the dye, and the facility with which it was applied, brought it into great vogue under the name of Saxon blue, from its origin. Its popularity in former times is evinced by the words of the old song, “The Blue Bells of Scotland:”—
“In what clothes, in what clothes is your Highland laddie clad?
His bonnet’s of the Saxon blue, his waistcoat of the plaid.” [6]
The Saxon blue consists simply of a solution of indigo, the Guatemala blue indigo being preferred, in sulphuric acid suitably diluted with water. The result of this reaction is not a single chemical substance, but two acids giving different tints, one called sulpho-purpuric acid or phenicine, and the other sulpho-indigotic acid; the first giving to wool a reddish-violet color, and the other a pure blue. A third compound has been indicated by Berzelius, the nature of which has not been determined. Whether one or the other of the two named acids, or the two combined, shall be produced by the reaction between the sulphuric acid and the indigo, depends upon the duration of the contact, the temperature of the mixture, and the nature and proportion of the acid used.
Persoz gives the following general receipt:—
| 1 | part by weight of | indigo, finely rubbed. |
| 1 | „ „ „ „ | Nordhaussen acid. |
| 1 | „ „ „ „ | ordinary sulphuric acid. |
Leave for forty-eight hours, then heat until a drop turned into water will dissolve without producing a precipitate. Leave to cool, and dilute with water till the strength is brought to 18 Beaumé.”
Napier says that he has found the following method of preparing sulphate of indigo, in quantities for use, very satisfactory: “The indigo is reduced to an impalpable powder, and completely dried by placing it on a sand bath or flue for some hours at a temperature of about 150° F. For each pound of indigo six pounds of highly concentrated sulphuric acid are put into a large jar, or earthen pot, furnished with a cover. This is kept in as dry a place as possible, and the indigo is added gradually in small quantities. The vessel is kept closely covered, and care taken that the heat of the solution does not exceed 212°F. When the indigo is all added, the vessel is placed in such a situation that the heat may be kept up at about 150°F., and allowed to stand, stirring occasionally, for forty-eight hours. These precautions being attended to, we have uniformly found that any failure occurring was clearly traceable to the impurity of the indigo or weakness of the acid used.”
The processes for producing and separating the two acids derived from the combination of sulphur and indigo are minutely given by Berzelius, in vol. i. of his “Traité de Chemie,” who states this curious fact illustrative of the peculiar affinities of wool with certain dyeing substances. Wool or flannel thoroughly scoured, when immersed in the blue solution of indigo with sulphuric acid, acts as a base: it combines gradually with the acid blue, and becomes itself colored of a deep blue. When saturated with color, it is withdrawn. Fresh wool is introduced until the bath yields no more color. If sublimed or perfectly pure indigo is used, there remains in the bath nothing but free sulphuric acid. The wool thus plays the part of a base with which the blue acids combine. The dyed wool is afterwards washed and treated in feeble alkaline bath (ammonia), which redissolves the blue. This method of purifying the Saxon blue is still practised by French manufacturers.
The combination of indigo with sulphuric acid, sometimes improperly called sulphate of indigo, is known by the dyers here and in England under the name of chemic. The name of chemic blue or green is also given the dyes formed from the indigo extract hereafter spoken of. It is largely used for making certain greens required in Scotch plaids.
The old Saxon blue or simple solution of indigo with sulphuric acid is now seldom prepared by the manufacturers themselves. It is now generally prepared for them, and furnished commercially under the name of indigo extract. The finer qualities used for fine dyeing and printing are known under the name of carmines of indigo, neutral extract, soluble indigo, ceruline, &c.
The production of indigo carmines, which are simply alkaline sulphindigotates or sulpho-purpurates, is founded upon their insolubility in a liquid charged with a salt.
If, for example, we dissolve one part of indigo in four parts of fuming acid, and dilute the liquid with sixty or eighty times its weight of water, it will contain, besides the sulphindigotic acid, an excess of sulphuric acid. By adding one part of crystals of soda so as to neutralize the bath, there will be formed not only sulphindigotate of soda, but sulphate of soda: as the former is insoluble in the saline liquid, the presence of the sulphate of soda causes the precipitation of the sulphindigotate in deep blue floccules. These are collected on woollen filters and washed to remove the sulphate of soda and a green coloring material, probably a modified chlorophyl, which the paste often contains, and which has the singular property of fixing itself on silk, but not on wool.
The carmines are divided according to their richness in indigo into simple carmine (4.96 per cent of indigo, water 89, saline materials 57), double carmine (10.2 per cent indigo, water 85, salts 4–8), triple carmine (12.4 per cent indigo water, 73.7, salts 13.9). A species of solid carmine known as Boiley blue or purple is in high repute in France.
The carmines may be tested by dyeing a specimen of wool in an acidulated bath to which cream of tartar has been added. The presence of the green matter, so objectionable to silk-dyers who make much use of these carmines, is detected by rubbing a small quantity of the carmine on a piece of glazed paper, which, when the color dries, gives a color varying from blue to a rich copper color: if any green coloring matter is left, it shows itself by a green aureola around the blue color. The method of applying the carmines in dyeing wool and silk,—for they are not adapted to cotton fabrics,—as given by M. de Kæppelin, is as follows:—
The operation is conducted in small wooden vats, provided with openings for manipulation, and pipes for inducting steam to heat the baths to the proper temperature. It consists of two parts, that of mordanting and dyeing. The former is thus conducted.
For each kilogram of tissue which has been previously scoured and bleached, there are provided 200 grammes of cream of tartar and 250 grammes of alum. These are dissolved in the bath of water of the vat, the temperature is raised to boiling heat, and the tissue is immersed in the bath f of an hour while it is worked over through the opening for manipulation. The pieces are then taken from the bath, to which is added a solution of the carmine in water containing a quantity of coloring matter proportionate to the intensity of the blue sought for. The solution ought to be prepared with care and passed through a silk sieve, so that the small insoluble grains which might have been left through bad fabrication may be left on the sieve. After the pieces have been manipulated in the colored bath, so as to exhaust the color and obtain the required blue, they should be rapidly washed in running water and dryed in the shade. Silk stuffs are dyed in the same way; but the alum should be previously applied cold by means of a saturated solution of alum, in which the stuffs should be immersed for an hour.
First sung by Mrs. Jordan, about the year 1799.