Scientific American 14, 4.10.1862
(Concluded from page 196.)
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Benzol is readily attacked by fuming nitric acid; it dissolves in it, producing a liquid of a deep red color. On addition of water this liwuid deposits a heavy yellow oil, collecting at the bottom of the cylinder, perfectly different from benzol, which floats on the surface of the water. The re-action will be intelligible to you, if I remind you that nitric acid when referred to our types, must be viewed as a water derivative; it is water in which, for one of the elementary hydrogen atoms, there has been substituted a compound atom, consisting of nitrogin and oxygen.
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Modern chemistry, you observe, returns to the conception of former ages, which, in the name aquafortis, appears to have anticipated in a measure our present notions.
When nitric acid acts on benzole and interchange takes place between the elementary atom of the latter and the compound atom of the former, nitro-benxole, the heavy yellow liquid which we have produced, and wter being formed:
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The hydrogen necessary for this transformation may be furnished by numerous processes. The most convenient method for our purpose consists in submitting nitro-benzon to the action of metallic iron and acetic acid, a process first proposed by M. Béchamp. I mix the three bodies in a glass retort, and on application of a gentle heat you observe how immediately a most powerful re-action manifests itself. Let us hasten to connect the retort with a condenser; I have removed the gas burner from the retort; nevertheless the re-action continues, and a considerable quantity of water, covering an oily layer, has already accumulated in the receiver. The oily liquid is aniline. We recognize it at once by its peculiar deportment with a solution of chloride of lime. On pouring a single drop of our distillate into this beaker which contains a soution of chloride of lime, a splendid purple cloud is almost instantaneously diffused throughout the liquid. You perceive we are approaching our subject. The beautiful color which aniline strikes with a solution of chloride of lime has been long known. A solution of bleaching powder has always been used as a test for aniline; indeed, it was by this color re-action that the presence of our compound in coal.-tar oil was first pointed out, a fact recorded in the name Kyanol (blue oil), originally given to aniline prepared from coal tar. Several other oxidizing agents, chromic acid for instance, were likewise known to produce colored compounds from aniline; but all the colors thus obtained were of a highly ephemeral character. Observe how the purple cloud which I produced by means of chloride of lime has rapidly changed to a dingy reddish precipitate. It was Mr. W. Perkin who had first the happy idea of investigating the circumstances under which this beautiful purple might be prepared in a form permanent and applicable for the purposes of the dyer. He succeeded in isolating this color by submitting, under appropriately selected circumstances, aniline to the action of bichromate of potassium and sulphuric acid.
Here then you have, step by step, the development of this new and important branch of chemical industry.
Through the kindness of my firend Mr. Perkin, I am enabled to exhibit to you magnificent specimens of his aniline purple, or mauve, in the dry state and in solution. This brown lump, with the remarkable coppery luster, is mauve in the solid state; its extraordinary tinctorial powers will be appreciated, if I tell you that this beautiful violet colored solution contains not more than 1/10th of a grain of mauve in one gallon of alcohol; you will also understand the considerable commercial value of this substance. Weight for weight, I am told by Mr. Perkin, this coloring matter, when pure, is sold at the price of metallic platinum.
Very little is known regarding the chemical nature of mauve; its composition is not yet made out, and, as a matter of course, the process by which it is formed from aniline remains as yet perfectly unexplained.
Magenta is one of the fancy names given to the splendid crimson which is likewise generated from aniline by the action of oxidizing agents. This substance was first observed in purely scientific researches, and more especially in the action of tetrachloride of carbon upon aniline. To a French chemist, M. Verguin, the merit is due of having for the first time obtained this substace on a larger scale; he produced it by the action of tetrachloride of tin on aniline. Numerous other processes were subsequently suggested, among which treatment of aniline with chloride or nitrate of mercury with arsenic acid, and many other sbstances may be mentioned. Magenta, often called fuchsine, roseine, &c., soon became an article of large consumption. A great impetus to this new branch of industry was given in France by Messes. Renard and Franc, who were the first to manufacture the new article on a commercial scale; in this country, very soon afterward, Messrs. Simpson, Maule and Nicholson engaged with great spirit in the manufacture of this splendid dye, the production of which has attained already colossal proportions. To Mr. E. C. Nicholson more especially belongs the credit of having developed this new industry to an undprecedented degree of perfection.
Before proceeding, however, let me show you the formation of Magenta by experiment. Among the many processes which I might adopt for this purpose I select the action of corrosive sublimate upon aniline, not because I consider this process superior to the others - it is, in fact, inferior to many - but because it is, perhaps, the best adapted for a lecture experiment. This white powder is chloride of mercury (corrosive sublimate); a small portion of this salt I mix in a test tube with perfectly colorless aniline. Let us stir the mixture with a glass rod until it is converted into a perfectly homogeneous liquid paste. This paste is still colorless, but on gently heating it by a gas burner it instantaneously assumes a splendid crimson of the greatest intentsity, a single frop of the liquid being capable of deeply coloring a large beaker filled with alcohol.
In all the processes which convert aniline into coloring matters, a considerable number of secondaty products are generated, which it is rather difficult to separate from the principal product of the rection. These difficulties have been most perfectly overcome by Mr. Nicholson, who has succeeded in obtaining Magenta in a state of absolute purity. Chemists have thus been enabled to analyze this substance, and to lift, at all events, the corner of the veil which still covers the mysterious formation of the colored derivates of aniline.
In the pure state, magenta is a fine crystalline, and, remarkably enough, perfectly colorless, or only slightly tinted body, which is represented by the formula-
C20H21N3O=C20H19N3,H2O.
Rosaniline (this is the name by which chemists designate the colorless body) is a base, or ammonia derivative, which forms a series of splendid salts. With hydrochloric acid, for instance, it produces a beautifully crystalline salt of the formula-
C20H19N3,Hcl
It is in the state of saline combination that rosaniline acts as a crimson dye. Into this shallow porcelain dish I have thrown a few crystals of rosaniline, which at a distance you scarcely perceive; I now pour upon these crystals a small quantity of acetic acid, when on gently beating the dish the crimson color instantaneously appears. But it is only in solution that even the salts of rosaniline are crmson colored; on slowly evaporating their solution, the red color entirely vanishes, and a splendid green crystalline substance remains, presenting in an extraordinary manner the beautiful metal uster which distinguishes the wings of the rose beetle. Together with all the products incolved in the manufacture of aniline and aniline dyes, my friedn Mr. Nicholson has placed before you the finest series of rosaniline salts which has ever been produced; and not content with this display, he was kind enough to send us a specimen of acetate of rosaniline, such as no mortal eye has ever seen before. The specimen may litterally called the "crown of magenta." Crowns are always expensive articles, and the cost and trouble of getting them are often greater than their actual value. This remark applied in a measure to the crown of magenta. For the benefit of those who are fond of big figures - and who is not a little afflicted with this weakness? - I may state that the crown was grown in a vessel containing not less than 8,000 l. worth of magenta, the crown itself being worth upward of 100l.
Having now explained the several stages of transition through which coal has to pass before it either becomes mauve or magenta, it may be of some interest to you to know the proportion in which the finished dye bears to the coal from which it is derived. A set of specimens for which I am likewise indebted to Mr. Nicholson, is most instructive in this respect. Observe, it sommences with a large mass of coal, weighing not less than 100 lbs.; the bottles which follow contain the coal-tar oil, napthts, benzol, nitro-benzol and aniline, obtainable in succession from 100 lbs. of coal; remark how they gradually diminish in size, and how small, I might almost say insignificant, appeart the bulk of magenta finally obtained. But compare the bulk of wool which this minute quantity will dye. It approximates to the bulk of coal with which we started. This comparison evinces, perhaps, sufficiently the extraordinary tinctorial power which this class of dye possesses, but a very simple experiment may possibly convey to you this idea even in a more impressive manner. The white paper which covers this large frame has been dusted over with a minute quantity of mauve; a second one is treated in a similar manner with magenta. The quantity of coloring matter is so small, that the paper has retained its original white color; but observe how it changes when I dash a beaker full of spirit against these squares; immediately the lovely purple of mauve is developed upon one of them, while the other one exhibits the dazzling crimson of magenta.
But let us now proceed to illustrate the mode of dyeing. For this purpose I introduce silk and wool, both unspun and woven, in succession, into solutions of mauve, of magenta, and, lastly, of a splendid new purple, lately discovered by Mr. Nicholson. Observe the extraordinary facility with which the coal tar colors are fixed both on wool and silk. These materials require no previous preparation, being dyed, in fact, simply by dipping, without the aid of any mordant. Silk and wool are animal substances; vegetal materials, such as cotton and linen, unless previously submitted to a special treatment, are scarcely affected by these dyes. This fact admits of being beautifully illustrated by dyeing linen fabrics on which ornaments have been embroidered in silk ribbon. The articles, when coming out of the bath, appear uniformly dyed; but by washing, first in pure water and then in dilute ammonia, the color rapidly vanishes from the linen ground, leaving the silk embroidery in brilliant colors. This extraordinary predilection of the aniline colors for animal substances is, moreover, strikingly illustrated by the condition of my hands, which by this time have acquired a throughly magentic appearance. Fortunately, the coal tar colors are unable to resist the action of chloride of lime, and I have therefore only to immerse my hands for a moment int o a solution of bleaching powder.
Alerady the color on my hand, you observe, has gone, but tith the color, I am afraid, my time too. Let me endeavor to bring this lecture to a conclusion. I have fulfilled in a measure the promise which I gave you at the commencement of this discourse. We have crossed together the extensive field which stretches between coal and color. I am impressed, deeply impressed, with the clumsiness of my performance as your guide, but I hope that the interest attached to the territory we have explored may, to some extent at all events, have indemnified you for the imperfection of my explanations, and that you leave the Royal Institution this evening with the kind of feeling every one of us has more than once experienced after traveling in similar company over a beautiful country - the guide is forgotten, but the impression of the scenery remains.
Having gone thus far, ou may think that it is fully time for me to make my bow. But I venture, even at this late hour, to dwell for a moment on the moral of the story which I have told you, though you may feel disposed to consider this story rather a highly colored one.
The material which I had to condense, I might almost say to force, into the short space of an hour, has been overwhelming; and whilst explaining the formation of the various substances which I had to describe, while illustraing their properties by experiment, I have scarcely had time to glance at the history of our subject. This hirstory is not without interest. You readily perceive that a branch of industry like the one I have endeavored to sketch could not possibly have risen like Minerva from the head of Jupiter - a sudden inspiration happily realized. The time, the toil, the thought of a host of inquiries were necessary to accomplish so remarkable an achievement. You cannot expect me at this late hour to examine minutely into this part of the subject, but I must not take leave of you without alluding to some facts which cannot fail to rivet the lively interest of the members of this institution. Let me tell you then that mauve and magenta are essentially Royal Institution colors; the foundation of this new industry was laid in Albermarle street. Benzol, which I have so repeatedly mentioned - benzol, which may be looked upon as the raw material, capable, under the influence of chemical agents, of assuming such wonderful shapes - benzol is the discovery of our great master, may I not add of our kind friend, Mr. Faraday. This volume, "The Philosophical Transactions for 1825," contains the description of his experiments. In 1825, thirty-seven years ago, the laboratory of the Royal Institution witnessed the birth of this remarkable body. Yesterday, under the auspices of Mr. Anderson, I invaded the same laboratory, a dilligent search was made, and in my hand I hold the trophies of our expedition, the original specimens of benzol which Mr. Faraday prepared. In thus reminding you of one of the early labors of Mr. Faraday - which, owing to the number and vastness of his subsequent discoveries, appears almost to have escaped from his memory like a tradition of years gone by - I have opened a glorious page in the glorious history of the Royal Institution. Benzol has furnished us mauve and magenta, but it has done much more than this. Ever since chemistry became endowed with this wonderful body, benzol has been the carrier of many of the leading ideas in our science. In the hands of Motscherlich, Zinin, Gerhardt and Laurent, in the lands of Charles Mansdield - never to be forgotten by his friends - and many others, benzol has been a powerful lever for the advancement of chemical science. Benzol and its derivates from one of the most interesting chapters in organic chemistry, the progress of which is intimately allied with the history of this compound.
But what has the history of benzol to do with the moral of mauve and magenta? Well, ladies and gentlemen, ask Mr. Faraday; ask him what in 1825 was his object in examining benzol. I have perhaps no right to answer this question in Mr. Faraday's presence; but I venture to say that we owe his remarkable inquiry to the pure delight he felt in the elaboration of truth. It was in the same spirit that his successors continued the work. Patiently they elicited fact after fact; observation was recorded after observation; it was the labor of love performed for the sake of truth; ultimately, by the united efforts of so many ardent inquiries, exerted year after year n the same direction, the chemical history of benzol and its derivates had been traced. The scientific foundation having thus been laid, the time of application had arrived, and by one bound as it were, these substances, hitherto exclusively the property of the philosopher, appear in the market place of life.
Need I say any more? The moral of mauve and magenta is transparent enough. I read it in your eyes - we understand each other. Whenever in future one of your chemical friends, full of enthusiasm, exhibits and explains to you his newly discovered compound, you will not cool his noble ardor by asking him that most terrible of all questions, "That is its use? Will your compound bleach or dye? Will its shave? May it be used as a substitute for leather?" Let him quietly go on with his work. The dye, the lather, the leather will make their appearance in due time. Let him, I repeat it, perform his task. Let him, indulge in the pursuit of truth - of truth pure and simple - of truth not for the sake of mauve, not for the sake of magenta - let him pursue truth for the sake of truth!
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