Creative Chemistry: Descriptive of Recent Achievements in the Chemical Industries

by Edwin E. Slosson

From Hesse's "The Industry of the Coal Tar Dyes," Journal of Industrial and Engineering Chemistry, December, 1914

The tar obtained from the gas plant or the coke plant has now to be redistilled, giving off the ten "crudes" already mentioned and leaving in the still sixty-five per cent. of pitch, which may be used for roofing, paving and the like. The ten primary products or crudes are then converted into secondary products or "intermediates" by processes like that for the conversion of benzene into aniline. There are some three hundred of these intermediates in use and from them are built up more than three times as many dyes. The year before the war the American custom house listed 5674 distinct brands of synthetic dyes imported, chiefly from Germany, but some of these were trade names for the same product made by different firms or represented by different degrees of purity or form of preparation. Although the number of possible products is unlimited and over five thousand dyes are known, yet only about nine hundred are in use. We can summarize the situation so:

Coal-tar → 10 crudes → 300 intermediates → 900 dyes → 5000 brands.

Or, to borrow the neat simile used by Dr. Bernhard C. Hesse, it is like cloth-making where "ten fibers make 300 yarns which are woven into 900 patterns."

The advantage of the artificial dyestuffs over those found in nature lies in their variety and adaptability. Practically any desired tint or shade can be made for any particular fabric. If my lady wants a new kind of green for her stockings or her hair she can have it. Candies and jellies and drinks can be made more attractive and therefore more appetizing by varied colors. Easter eggs and Easter bonnets take on new and brighter hues.

More and more the chemist is becoming the architect of his own fortunes. He does not make discoveries by picking up a beaker and pouring into it a little from each bottle on the shelf to see what happens. He generally knows what he is after, and he generally gets it, although he is still often baffled and occasionally happens on something quite unexpected and perhaps more valuable than what he was looking for. Columbus was looking for India when he ran into an obstacle that proved to be America. William Henry Perkin was looking for quinine when he blundered into that rich and undiscovered country, the aniline dyes. William Henry was a queer boy. He had rather listen to a chemistry lecture than eat. When he was attending the City of London School at the age of thirteen there was an extra course of lectures on chemistry given at the noon recess, so he skipped his lunch to take them in. Hearing that a German chemist named Hofmann had opened a laboratory in the Royal College of London he headed for that. Hofmann obviously had no fear of forcing the young intellect prematurely. He perhaps had never heard that "the tender petals of the adolescent mind must be allowed to open slowly." He admitted young Perkin at the age of fifteen and started him on research at the end of his second year. An American student nowadays thinks he is lucky if he gets started on his research five years older than Perkin. Now if Hofmann had studied pedagogical psychology he would have been informed that nothing chills the ardor of the adolescent mind like being set at tasks too great for its powers. If he had heard this and believed it, he would not have allowed Perkin to spend two years in fruitless endeavors to isolate phenanthrene from coal tar and to prepare artificial quinine—and in that case Perkin would never have discovered the aniline dyes. But Perkin, so far from being discouraged, set up a private laboratory so he could work over-time. While working here during the Easter vacation of 1856—the date is as well worth remembering as 1066—he was oxidizing some aniline oil when he got what chemists most detest, a black, tarry mass instead of nice, clean crystals. When he went to wash this out with alcohol he was surprised to find that it gave a beautiful purple solution. This was "mauve," the first of the aniline dyes.

The funny thing about it was that when Perkin tried to repeat the experiment with purer aniline he could not get his color. It was because he was working with impure chemicals, with aniline containing a little toluidine, that he discovered mauve. It was, as I said, a lucky accident. But it was not accidental that the accident happened to the young fellow who spent his noonings and vacations at the study of chemistry. A man may not find what he is looking for, but he never finds anything unless he is looking for something.

Mauve was a product of creative chemistry, for it was a substance that had never existed before. Perkin's next great triumph, ten years later, was in rivaling Nature in the manufacture of one of her own choice products. This is alizarin, the coloring matter contained in the madder root. It was an ancient and oriental dyestuff, known as "Turkey red" or by its Arabic name of "alizari." When madder was introduced into France it became a profitable crop and at one time half a million tons a year were raised. A couple of French chemists, Robiquet and Colin, extracted from madder its active principle, alizarin, in 1828, but it was not until forty years later that it was discovered that alizarin had for its base one of the coal-tar products, anthracene. Then came a neck-and-neck race between Perkin and his German rivals to see which could discover a cheap process for making alizarin from anthracene. The German chemists beat him to the patent office by one day! Graebe and Liebermann filed their application for a patent on the sulfuric acid process as No. 1936 on June 25, 1869. Perkin filed his for the same process as No. 1948 on June 26. It had required twenty years to determine the constitution of alizarin, but within six months from its first synthesis the commercial process was developed and within a few years the sale of artificial alizarin reached $8,000,000 annually. The madder fields of France were put to other uses and even the French soldiers became dependent on made-in-Germany dyes for their red trousers. The British soldiers were placed in a similar situation as regards their red coats when after 1878 the azo scarlets put the cochineal bug out of business.

The modern chemist has robbed royalty of its most distinctive insignia, Tyrian purple. In ancient times to be "porphyrogene," that is "born to the purple," was like admission to the Almanach de Gotha at the present time, for only princes or their wealthy rivals could afford to pay $600 a pound for crimsoned linen. The precious dye is secreted by a snail-like shellfish of the eastern coast of the Mediterranean. From a tiny sac behind the head a drop of thick whitish liquid, smelling like garlic, can be extracted. If this is spread upon cloth of any kind and exposed to air and sunlight it turns first green, next blue and then purple. If the cloth is washed with soap—that is, set by alkali—it becomes a fast crimson, such as Catholic cardinals still wear as princes of the church. The Phœnician merchants made fortunes out of their monopoly, but after the fall of Tyre it became one of "the lost arts"—and accordingly considered by those whose faces are set toward the past as much more wonderful than any of the new arts. But in 1909 Friedlander put an end to the superstition by analyzing Tyrian purple and finding that it was already known. It was the same as a dye that had been prepared five years before by Sachs but had not come into commercial use because of its inferiority to others in the market. It required 12,000 of the mollusks to supply the little material needed for analysis, but once the chemist had identified it he did not need to bother the Murex further, for he could make it by the ton if he had wanted to. The coloring principle turned out to be a di-brom indigo, that is the same as the substance extracted from the Indian plant, but with the addition of two atoms of bromine. Why a particular kind of a shellfish should have got the habit of extracting this rare element from sea water and stowing it away in this peculiar form is "one of those things no fellow can find out." But according to the chemist the Murex mollusk made a mistake in hitching the bromine to the wrong carbon atoms. He finds as he would word it that the 6:6' di-brom indigo secreted by the shellfish is not so good as the 5:5' di-brom indigo now manufactured at a cheap rate and in unlimited quantity. But we must not expect too much of a mollusk's mind. In their cheapness lies the offense of the aniline dyes in the minds of some people. Our modern aristocrats would delight to be entitled "porphyrogeniti" and to wear exclusive gowns of "purple and scarlet from the isles of Elishah" as was done in Ezekiel's time, but when any shopgirl or sailor can wear the royal color it spoils its beauty in their eyes. Applied science accomplishes a real democracy such as legislation has ever failed to establish.

Any kind of dye found in nature can be made in the laboratory whenever its composition is understood and usually it can be made cheaper and purer than it can be extracted from the plant. But to work out a profitable process for making it synthetically is sometimes a task requiring high skill, persistent labor and heavy expenditure. One of the latest and most striking of these achievements of synthetic chemistry is the manufacture of indigo.