Aniline Colors.

Manufacturer and Builder ?, 1872

By Prof. C. F. Chandler.

It is well understood that coal is an element of our national wealth; and that we derive from it our power. The combustion of three hundred pounds of coal under a steam-boiler will produce a power equal to the mechanical force exerted by a man for a year. Another important application of bituminous coal is to the manufacture of illuminating gas. In this manufacture there are certain residual products which were at first were thrown away; and these I propose to treat of.

Coal-tar is produced at the rate of about ten gallons to the ton of coal. Thousands upon thousands of barrels of coal-tar were at first thrown away; but when the chemist turned his attention to this substance, he discovered so many products useful in the arts which could be made from it, that coal-tar now finds a ready market at $1.50 per barrel. When coal-tar is subjected to distillation, the liquid portion passes off, and there remains the heavy black pitch which is used for roofing and for pavements. The liquid portion, which comprises about one fourth of the original coal-tar, produces first a light fluid called naphtha, and then a heavy liquid which is called dead oil. The light liquid is a mixture of carbon and hydrogen, of which benzole is the type. It is C12H6; that is, taking into account the difference of weight, seventytwo Parts of carbon to six parts of hydrogen. Other substances are produced from this differing by two atoms of each, making C14H8, C16H10, C18H12, C20H14, etc.; but until recently, only the first two of these had any practical importance in the arts. They were used simply as fuel, and as antiseptics for preserving timber from decay. But lately one of them is claimed to be a specific for the small-pox.

After the volatile portions have been removed, there remains this dead oil, which is heavier than water. This was for a long time used as a fuel in glass-houses. It was then found that the carbolic acid it contains was a most powerful disinfectant and antiseptic. It was found that it would prevent the spread of the cattle disease; that cattle having the disease in its worst form might be placed with others with safety, if they were protected by this acid. It was found too that the durability of timber was increased four or five fold by its application.

The beautiful colors which have recently been obtained from refuse coal-tar are subdivided into three groups, the aniline colors, those derived from naphthaline, and the carbolic acid colors. I shall confine this article to the chemical phase of the subject.

Benzoic is a hydrocarbon. Bringing that in contact with nitric acid, an atom of nitrogen carries off an atom of hydrogen, and we have nitrobenzole, which is a very fragrant oil, an artificial oil of bitter abounds, used instead of that substance in the manufacture of soaps. When the nitrobenzole is made to give up its oxygen and take up hydrogen, it becomes aniline.

Nitrogen is a protean element which gives rise to a great variety of compounds. Ammonia is NH3, and these three atoms of hydrogen can be replaced by a great variety of substances. Aniline is a similar substance. It is ammonia, replacing one atom of hydrogen by phenyl, which is C12H5. There is no limit to the number of compounds that may be de i veloped on this type; and it opens one of the most important fields of chemical investigation at the present day. All the aniline colors are derived from N30H9, converted by the process of substitution into new compounds. The first investigation in tide direction, which however did not result in any practical product, was that of a German chemist, who found that by treating aniline with chloride of lime, he produced a violet or purple tint. Perkins, who was the first successful manufacturer of color from coal-tar, manufactured a substance to which lie gave the name of mauve. Then came the discovery of the roseaniline, which is produced from commercial aniline, pure aniline not answering the purpose. Subjecting commercial aniline to the action of nitric acid, and then to the action of nascent hydrogen, we obtain roseaniline, which is C40H19N3. The chloride, hydrochlorate, arseniate, acetate, nitrate, and other salts of aniline produce most beautiful tints. Hoffmann found that he could change the red tint of the roseaniline to various shades of violet, by simply boiling it with more aniline. This introduced more phenyl in the place of hydrogen. One atom made it purple, another more blue, and a third atom of phenyl made it the most beautiful blue that has ever been manufactured.

Replacing the hydrogen with ethyl C4H15, or with methyl C2H3, we obtain still further colors. In every case the beautiful rose red becomes more and more purple, until the substitution of the last atom of hydrogen converts it into a deep and perfect blue. On carrying the investigation further, it was found that by proper treatment the blue color could be converted into a green, by using ethyl and methyl. Subsequent treatment developed an entirely different base, having the form C40H17N3, with yellow tints; and further treatment produced a brown and finally a black; so that the most durable black for calico printing is now obtained from aniline.

From the coal-tar obtained from a ton of coal, three fourths of a pound of this beautiful color are produced. The coal, which is worth about $6, produces the gas, the coke, the ammoniacal water, largely used for agricultural purposes, the carbolic acid, used for the preservation of timber and as a disinfectant, and finally this beautiful color, which alone is worth nearly as much as the coal originally cost. The amount of this industry has become no enormous that at present five tons of this raw aniline oil are manufactured daily, on the continent alone, and ninety thousand pounds of iodine are used in effecting the substitution; and yet it is an industry which has started since 1860.

In regard to the carbolic acid colors, they are obtained by treating the dead oil with an alkali. This furnishes a number of coloring matters. Carbolic acid is C12H6O2; or it is the oxyd of benzole, which is C12H6. Treating carbolic acid with nitric acid, we produce C12H3 (NO4)3 O2. Picric acid is a substantive dye for silk and wool, uniting with them without any mordant. Treating picric acid with the cyanide of potassium, an acid is produced which gives beautiful garnet colors on silk and wool. By treating carbolic acid with soda and the oxyd of mercury it is converted into rosolic acid, which produces various shades of orange, and is used for coloring house paper. Treating this with ammonia, it produces a scarlet tint. The intimate connection existing between the rosolic acid and the aniline colors, is shown by the fact that by treating roseaniline with anhydrous acid, the same result is obtained. From this orange red of rosolic acid can be produced a deep blue color by the action of aniline.

There is also a series of naphthaline colors, but they are not found to be fast.

When coal-oil is distilled, and 25 or 30 per cent of volatile products are removed, the result is solid, and is called anthracene. Recently, from this there has been artificially produced the coloring matter of madder. The colors from aniline had proved brilliant and durable for silk and wool, but not for cotton fabrics. It is now a question whether the colors from anthracene will supply this want, whether they will be found to be permanent.

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