Dyeing for blue jeans Page 9

December 1986

Natural Dyes Compounds from snails and dried insects adorned the rich and famous. 4 Blue Jeans Denim, which started as a common French cloth, has evolved into every man’s 9 high-fashion fabric.

MysteryMatters Flash Point! 10 Everyone knew that No. 6 fuel oil couldn’t explode. Everyone was wrong.

Experimenter’s Notebook Natural Dyeing 12 Bored with white socks? Boil them in dandelions!

The Back Burner Going Against the Flow: The Isolation of Fluorine 13 A reactive element plays “hide and seek” with would-be discoverers.

The Price of Progress Ancient man washed clothes by pounding them with a rock. Modern man 16 pays $6 for the rock. NATD DYEs

by Clair G. Wood their coloring agents exclusively from rocks and salts, and earth tones pre­ Thou shalt make the tabernacle with dominated-until weaving was in­ ten curtains of twisted linen, and blue vented. and purple and scarlet . ... Pigments had been made by com­ -Exodus 26:1 bining colored minerals with a vehicle, such as oil or mud, that would adhere The human race has always been to a surface. When the pastelike pig­ fascinated with color. As early as ments were applied to fabric, the 180,000 B.C., the Neanderthal tribes cloth became stiff, and the coloring prepared their dead for burial by coat­ material soon washed or fell out. Pig­ ing them with red ochre (iron [III] ox­ ments wouldn't work-cloth could ide). Their successors, the Cro­ only be colored by dyes, organic Magnon peoples, made elaborate molecules that bond directly to the cave paintings using yellow and red textile. iron oxides, black manganese diox­ ide, and white clays. For tens of thou­ Animal dyes I sands of years, humans obtained One of the earliest and most impor­ 0 OH 0 tant of the animal dyes came from II I C-CH3 I several species of snails found along ,. the shores of the Mediterranean. Tyrian purple (Figure 1) was discov­ OH ered by the Phoenicians about 1500 COOHO OH B.C. and became, for the next 3000 years, the most important dye of the

L ~. .-' ..__... Figure 2. Kermesic acid, derived from Br the kermes insect, so impressed Pope

civilizations that rose and fell in the Br area. The mollusks were avidly gath­ ered as dye factories sprung up along the Mediterranean and west African coasts, and Phoenician traders car­ ried the dye to Spain, France, and Italy. According to Pliny the Elder (ca. 50 A.D.), the dye was extracted by crushing the shellfish and boiling them in salt water for ten days. Cloth was dipped in this solution, then ex­ posed to sunlight. The yellow color changed to greenish-blue, then to purple. The Roman emperors prized the dye and decreed that only mem­ bers of the royal family could wear clothing colored by it, hence the ex­ pression "born to the purple." Among tl10se who wore Tyrian purple were Figure 1. Tyrian purple, which is known chemically as 6,6'-dibromoindigo, is an ancient dye that was extracted from a Mediterranean mollusk. The Roman Empire Alexander the Great, Julius Caesar, decreed that only members of the royal family (such as Julius Caesar, above) and Cleopatra. could wear robes dyed with Tyrian purple. Other animal dyes were obtained 4 brought it to Europe, where it rapidly replaced kermes. The scarlet ob­ tained with a tin mordant is particu­ larly beautiful and was used until 1954 to dye the uniforms of the Brit­ ish Brigade of Guards uniforms.

Vegetable dyes Vegetables dyes can be found in almost any plant. Historically, three of the most important were madder, woad, and indigo. Madder (Rubia tinctorum), a bright red dye, comes from a plant of the same name also known as "dyer's root." Though its origin is lost in antiq­ uity, it was used to dye the wrappings on Egyptian mummies. It is said that Alexander the Great used madder to help him defeat the Persians in 350 B.C. He had many of his soldiers dye their cloaks with splotches of red and stagger onto the battlefield. As the jubilant Persians fell on the "badly wounded" enemy, they were soundly defeated. Madder appeared in Eu­ rope in the seventh century and was the dominant red dye for more than Palinl (1467 A.O:) "that'he chose'It"for 1000 years. It provided the red for the the scarlet of the cardinals' robes. famous British redcoats during the American Revolution. The chemical from insects. Kermes (Figure 2) was a scarlet dye obtained from Coccus i1icis, a tree scale that lived on oak. OH 0 Moses mentioned its use in Egypt, and other writers referred to it as captured booty in 1400 B.C. Kermes varied in color from bluish-red to brib liant scarlet depending on the mor­ dant used (more about mordants below). A dye very similar to kermes was discovered by Mexican dyers around 1000 B.C. Cochineal (Figure 3) is de­ rived from another scale insect, Dac­ tylopius coccus, that lived on cactus. The insects were collected by hand, about 200 pounds per acre of cactus, and dried in the sun. The dried in­ sects resembled rust-colored grain seeds and gave scarlet dye when soaked in water. The Spaniards Figure 3. The red dye cochineal is extracted from insects that live on the Opuntia learned of cochineal in 1518 A.D. and cactus. About 70,000 insects-female only-are needed to make a pound of dye. Chromophores Why do certain compounds make good dyes? In part because they contain chromophores. Chromo­ phores (Greek: chroma = color; phores = bearer) are groups of atoms within organic moleculeS that selectively absorb visible light. When light of certain colors strikes the chromophores, electrons are energized and the light is ab­ sorbed. Light of other colors is reflected to the observer. Below are a few of the chemical groups that can serve as chromophores.

-N=N- azo

carbonyl

\/ C=C ethylene / "

II -C=C-C=C- polyenes II o Madder plant and root responsible for the color is alizarin Figure 4. The color of alizarin was close nitro (Figure 4). The natural dye qUickly enough to that of blood that the lost favor in the late nineteenth cen­ soldiers of Alexander the Great used it to make phony wounds. Unlike most " / tury as it was replaced by the C=C ancient dyes, the synthetic version of / \ cheaper synthetic version of the same alizarin is still used commercially. =C C= quinoid compound. "C=C/ When Julius Caesar arrived in Brit­ / " ain in 55 B.C., he described the fierce on some of the most ancient textile warriors he found there: "All Britons fragments ever unearthed. It was To make a good dye, it is not stain themselves with woad which used to dye the robes of the high enough for a compound to be col­ grows wild and produces a blue color priests of Jerusalem in Biblical times, orful. It must also be soluble in which gives them a terrible appear­ but it was in Europe that it was exten­ water so that its solution can pene­ ance in battle." Nor was it only the sively cultivated. The dye was ob­ trate the fabric. Once in the fibers, warriors who painted themselves tained by first air-drying the woad it must become insoluble, or attach blue, for Pliny the Elder writes, plants and grinding them to a powder. tightly to the fibers, so it does not "There is a plant like plantain, the The powder was then moistened, wash out. These requirements led juice of which the wives and daugh­ placed in a warm, dark place, and natural dyers to use mordants and ters of Britain paint themselves and stirred frequently. Several weeks of vat dyeing. Other techniques are go naked resembling Moors and Ethi­ fermentation produced a black paste, used in modern commercial dye­ opians." from which a blue dye was extracted. ing. Woad, a dye from the European The European woad plant had indigo plant Isatis tinctoria, has been found (Figure 5) as its main chemical con-

6 Mordants To make a good dye, it is not enough for a compound to be col­ orful. It must also be soluble in water so that its solution can pene­ stituent. Woad was the principal Euro­ ful was the anti-indigo lobby that the trate the fabric. Once in the fibers, pean dye for centuries, and dyers dye did not become established in it must become insoluble, or attach ' became quite skilled at mixing it with Europe for more than 500 years. tightly to the fibers, so that it does :~ ~ other dyes to obtain new colors. Then King George II chose indigo for not wash out. These requirements \ ~ ~ Saxon green was the result of dyeing the British naval uniform, giving the led natural dyers to use mordants a fabric with woad, then overdyeing it world "navy blue" forever after. Indigo and vat dyeing (see "Indigo," p. 8). ~...... ,' with weld, a yellow dye from another was one of the few natural dyes of Other techniques are used in mod­ .·'w' plant. When woad was overdyed with commercial importance to America. ern commercial dyeing. madder, a purple shade resulted. In 1744 Eliza Pickney grew indigo A mordant is a coupling agent. Indigo, from the plant Indigofera from seeds her British army officer Usually a metal ion, it attaches to tinctoria, is much richer in the indigo father brought from the East Indies to both the dye and the fiber and molecule. This dye worked its way the colonies. Later, the enterprising forms a link between them. A mor­ from India to Egypt, the Holy Lands, young woman persuaded plantation dant can fix a dye that would other­ and eventually Europe, where it ar­ owners around Charleston, S.C., to wise come off in the wash. Most rived around 1200 A.D. Its introduction grow indigo and set up the Winyah mordants are salts of chromium, was bitterly opposed by woad Indigo Society. This cooperative aluminum, copper, ammonium, growers. Many laws were passed shipped great quantities of the dye to iron, and tin. In addition to binding against use of the "devil's dye," and England, until introduction of syn­ the dye to the cloth, some mor­ it was widely believed to harm both thetic indigo destroyed the market for dants change its color as well. the cloth and its wearer. So success- the natural product. Today indigo has Alizarin, the crimson color of the British "redcoat," turns rose color when mordanted with aluminum, purple-red with calcium, and violet with magnesium. In this diagram, a chromium ion forms coordinate covalent bonds with electron pairs on the dye and protein molecules.

, / , / 'cf / / o ·0··'""/ H-"""" "-. c~ .}

Some effective mordants include potassium aluminum sulfate, KAI(S04h (sometimes called alum); potassium dichromate, K2Cr207 (chrome mordant); iron (II) sulfate, FeS04 (iron mordant); copper (II) sulfate, CUS04 (copper mordant); Figure 5. At one time, British dyers could be hanged for using imported indigo instead of native woad, even though both contained the same dye molecule. and tin (II) chloride, SnCl2(tin mor­ Later, all British naval uniforms (such as the one worn by Horatio Nelson, above) dant). were dyed with indigo, which became known as "navy blue." 7 been largely replaced by other blue man-made dyes on the natural dye dyes, though it is still used in cosmet­ market was devastating. No better ics (0 &C Blue #6), as a laboratory example can be found than the story indicator solution (indigo blue), and as of indigo. In 1893, India had 76 indigo the dye of choice for coloring blue factories and 250,000 acres of the jeans. plant under cultivation. In 1883, Adolph von Baeyer (who started his Synthetic dyes chemistry career at age 13) synthe­ The synthetic dye industry began sized the indigo molecule. His with a serendipitous discovery. In method was not economical, but it 1856, William Perkin, an 18-year-old paved the way for chemists at the student at the Royal College of German BASF Corporation to find an Chemistry in London. was tryina to alternate route, and synthetic indigo was marketed in 1900. The market for Indigo natural indigo collapsed almost over­ night. Today more than 6000 synthetic Because indigo is not soluble in Figure 6. Mauve started a purple dyes are available, and most are water, it is applied by a multistep fashion fad among Victorian women. cheaper and more effective than the process known as vat dyeing. The The first synthetic dye to be dyes found in nature. However, for indigo (A in the diagram below) is commercially successful, mauve marked the beginning of the end for craftsmen and amateur scientists, first chemically reduced to a form dyes derived from plants and animals. natural dyes still have one major ad­ that is colorless but soluble (B). vantage-they are as close as the Traditionally. this reduction was garden. . synthesize quinine, a drug used to done by fermentation or treatment treat malaria, by reacting aniline sul­ with urine, but today it is done by Clair G. Wood teaches chemistry at East­ fate with potassium dichromate. He application of sodium hydrosulfite. ern Maine Vocational Technical Institute in obtained a black paste which, when The cloth is soaked in this pale Bangor, Me. He has also written for Chem extracted with alcohol, gave a violet Matters on soap (February 1985) and yellow solution, then "skyed" by residue that dissolved in water to give detergents (Apri/1985). hanging it in the air. Oxygen in the a brilliant purple color. Perkin ob­ air oxidizes the indigo back to the served that the dye had a strong affin­ References brilliant blue form (C), which is Leggett, William F. Ancient and Medieval Dyes; ity for silk. He quickly realized the insoluble and difficult to dislodge Chemical Publishing Company, Inc.: New commercial possibilities and left col­ from the fibers. York,1944. lege to go into business for himself. Kierstead, Sallie P. Natural Dyes; Bruce Hum­ phries, Inc.: Boston, 1950. The dye, mauve, (Figure 6) rapidly Krochmal, Arnold; Krochmal, Connie. The proved to be a commercial success; Complete Illustrated Book of Dyes from Queen Victoria preferred mauve­ Natural Sources; Doubleday &Company, Inc.: Garden City, N.Y., 1974. colored silk for her gowns. Perkin's Fleming, Stuart. "The Tale of Cochineal: discovery was even more fortuitous Insect Farming in the New World," than it first appeared. If his aniline Archaeology, September/October 1983. "Blue-Purple Dye of Antiquity Reborn," Sci­ had not been contaminated with to­ ence News 1984, 126, 148. luidine, an essential step in the syn­ Crowell, Carolyn. "Color from the Fields," thesis of mauve could not have taken Chemistry 1973, 46(9),14-17. "Natural Plant Dyeing"; Brooklyn Botanic place. Perkin's discovery opened the Gardens: Brooklyn, N.Y.; Publication No. 72. floodgates for similar research "Dye Plants and Dyeing"; Brooklyn Botanic throughout Europe. By 1870, cloth Gardens: Booklyn, N.Y.; Publication No. 46. "Colors for Textiles," J. Chern. Ed. 1947,24, could be purchased in many more 2-10. colors than was ever possible with Decelles, Corinne. "The Story of Dyes and natural dyes. Dyeing," J. Chern. Ed. 1949,26,583-87. "Dyeing Synthetic Fibers," Chern. & Eng. Initially the British were the leaders News, 1956,34,4358-61. in factory-produced dyes, but the Ziderman, Irving. "Biblical Dyes of Animal Germans soon dominated the field, Origin," Chemistry In Britain, May 1986. Schultz, Kathleen. Create Your Own Natural obtaining 950 patents between 1880 Dyes; Sterling Publishing Company: New and 1900. The effect of this deluge of York,1982.

8 by David P. Robson

The California gold rush attracted adventurers and entrepreneurs from around the world. In 1850, a Bavarian tradesman named Levi Strauss ar­ rived in San Francisco carrying some canvas for making tents. Noticing that the. miners needed sturdy trousers, he manufactured a few pairs and dyed them with indigo. They sold quickly. When the miners-who over­ stuffed their pockets with gold ore­ complained that the pants pockets ripped out, Levi reinforced them with copper rivots. The Levi's gained a reputation for being durable and com­ fortable. The comfortable cotton fab­ ric-originally from the French town of Nimes-was called serge de Nlmes, which Americans soon shortened to "denim."

Denim Today, cotton is woven and dyed in special ways to make denim. Most textiles are colored by soaking them thoroughly in dye. The material is passed through the dye tank slowly so that the dye solution can penetrate and color the fibers in the core of the Gold miners working the Last Chance mine in Placer County, Calit, pose in their yarn. Denim is done differently. Levi's jeans in 1882. (Photo, Levi Strauss & Co.) In the North Carolina denim mills, cotton yarn is unwound from large quick dip followed by air oxidation-is has a pleasing light hue. The back spools and passed quickly through a repeated as many as 8 times. The side of denim is one-quarter blue and vat of indigo, a pale yellow solution. color grows darker with each treat­ three quarters white. Roll up your The yarn is dipped for only 20 sec­ ment and soon reaches the familiar jeans and take a look. onds so that it will not be wet thor­ jeans blue. However, underneath it oughly. The yarn turns lemon-yellow, all, the core of the yarn is still white. Old, friendly jeans with the dye covering only the sur­ The spools of blue yarn are trans­ As your jeans age, the blue gets face. As the yarn moves along over­ ferred to the loom where they are lighter. To some extent, the indigo head rollers, the dye is oxidized by woven together with undyed yarn. simply washes out of the fabric (it is the air and, within one or two min­ The blue yarn makes up the warp, the not as "fast" as more modern dyes), utes, turns pale blue (see "Indigo," p. vertical rows in the fabric, and the but most of the "fading" is caused by 8). The moving line of yarn dips into white yarn makes up the horizontal abrasion. The areas that get a lot of another indigo vat for 20 seconds and filling. Instead of the simple over-un­ wear-knees, edges of the pockets­ emerges-green. This colorful sur­ der-over-under pattern, the loom is grow lighter because the fibers near prise is created when the pale blue set for a three-an-one twill weave. The the surface of the yarn rub off, expos­ yarn is covered with the yellow dye warp passes over three strands of ing the white cotton below. If your solution. Within minutes, the green filling, then under one, over three, jeans don't wear fast enough, you turns to a darker blue as the second under one. Because every fourth can "stone wash" them at home (see layer of dye oxidizes. This process- strand is white, the dark blue fabric back cover).

9 ______MYSTE61

FLASH POINT! they cleaned away rust that had adjuster, I went to the tank farm to by Charles F. Rowell formed since Monday and were ready search for the cause of the accident. to weld on the patch. The tank con­ When I arrived, the operators were It was a beautiful spring day, with the tained NO.6 fuel oil, a black viscous pumping the oil out of the damaged clarity that comes from recent rains. fluid that was "well known" to be of tank into a holding tank while search­ From the tank farm, workers could little hazard to welders. The head ing for the third welder. They recov­ see to the far side of the Baltimore welder lit his torch. ered his body from the oil in the dam­ harbor. When petroleum is unloaded There was an explosion, and the aged tank. I climbed to the top of the from oceangoing ships, it is stored at tank erupted in flames. The top of the holding tank to take some photo­ the tank farm in dozens of squat, tank, made of steel plates 1f2-inch graphs. Near the vents at the top of cylindrical tanks. Each tank is about thick, was ripped apart like tissue the holding tank, I smelled hydrocar­ 45 feet high and 100 feet in diameter paper. The welders were thrown into bon fumes and noticed that water was and is surrounded by a containing the air. Two of them landed in a pool condensing where vapor escaped wall-an earthen dike that would of rainwater that had collected behind from the vents. At the time, I attached catch oil should the tank leak. the containing wall. The water cush­ little significance to these observa­ On Wednesday morning, three ioned their fall, and they both sur­ tions. welders carrying heavy equipment vived. The third welder was missing. A couple of days later, the answer struggled up the stairs to the top of The fuel oil burned for more than ten hit rne. Since the oil had not only the containing wall. They crossed a hours before the fire department was ignited but had continued to burn, short catwalk, then climbed a final able to extinguish the blaze. Investi­ some specific chemical conditions section of stairs to the top of the tank. gators from the U.S. Coast Guard and must have been present. I called the Two days before, they had cut a hole the fire marshal's office found "no tank farm operator and asked him if in the top of the tank and installed a apparent explanation" for the acci­ he had moved any fuel oil out of the depth-measuring system. Today, they dent. They agreed that NO.6 fuel oil tank before the fire. He had indeed. planned to complete the job by patch­ is not explosive. The mystery was solved. ing an extra hole. Using a grinder, At the request of the insurance As your nose tells you, petroleum

Pressure points When liquid fuel is sealed in a Vapor pressure container with air, the pressure inside will rise as some of the fuel molecules evaporate (upward ar­ row in A, below). The vapor pres­ sure will level off (B) when the gas­ eous fuel molecules become sufficiently concentrated that the vapor condenses (downward ar­ row) at the same rate that the liq­ uid evaporates. If the fuel is heated (C), evaporation will accelerate, the fuel molecules in the gas phase will become more concentrated, and the vapor pressure will in­ crease. When the liquid reaches a tem­ perature called the flash point, the vapor-air mixture is concentrated enough to burn if ignited, and the fuel will vaporize fast enough to sustain the fire. In the accompany­ ing story, the No.6 fuel oil was well A B above the flash point. c lU •

-,---.---" ._-_ ...-

) ~ ~,~~_~-~~ ~_~ ~_~~Jr-=~.~.~ , __ __

Cutaway drawing of the 011 storage tank. An earthen dike surrounds the tank. When No.6 fuel 011 is cold, it is too viscous to flow. Before It can be pumped out of the tank, the 011 must be heated by the steam pipes at the bottom of the tank (interior view).

fuels like gasoline or kerosene give oil had been pumped out of the tank the temperature of the oil must have off vapor. In a petroleum fire, it is the the day before. Because it is very been well above the flash point be­ vapor, not the liquid fuel, that burns. viscous, NO.6 oil must be heated cause-as the water escaping from When a fire burns over a liquid fuel before it can be pumped. Although the vents of the holding tank indi­ the vapor is consumed rapidly. If the the heaters had been turned off Tues­ cated-the firefighters had flooded vapor is not replaced by further eva­ day night, the oil had not cooled the oil with water but were unable to poration of the liquid, the fire will go much in the intervening twelve hours. cool it below the flash point for many out almost as soon as it starts. If the When the welders lit their torch, the hours. liquid can replace the vapor as fast as oil was above the flash point. There Although there was a thermometer it is burned, the fire will continue. The was a lot of vapor mixed with the air on the opposite side of the tank, it rate at which a liquid gives off vapor in the tank-the combustion of this was of no value to the welders be­ increases as the temperature goes mixture provided the energy that de­ cause they did not know the flash up. The lowest temperature at which stroyed the tank. Furthermore, once point of NO.6 oil. Most of the opera­ a particular fuel can sustain a fire is the flame was ignited, the hot oil sup­ tors around the tank farm knew the called the flash point (see box, "Pres­ plied vapor at such a rate that the fire word "flash point" but did not know sure Points," p. 10). burned tenaciously for hours. In fact, what it meant in practical terms. This The welders first worked on Mon­ was a demonstration they would day. The tank farm had not been ac­ Flash points of some never forget. tive all weekend, and the oil was well common liquids (OC) below the flash point. There was no Charles Rowell has worked at the Office danger of a fire. Even if ignition had of Naval Research (Chicago) and taught at Gasoline -43 occurred, the burning would have the U.S. Naval Postgraduate School (Mon­ Isopropyl alcohol 12 terey, Calif). Currently he is on the faculty used up all the available vapor and Kerosene 38 of the U.S. Naval Academy (Annapolis, would have gone out very quickly. NO.6 fuel oil 66 Md.) and is a consultant for Forensic Tech­ The welders returned to the job on nologies International, which asked him to Wednesday. In the meantime, some investigate this case. 11 I

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GOING AGAINST THE FLOW: chemical methods that had produced THE ISOLATION OF elemental chlorine. All failed to yield FLUORINE fluorine. Davy then turned to the by Derek A. Davenport "great Voltaic batteries of the Royal Institution," which only a few years The element fluorine challenged nine­ earlier had provided the electricity he teenth-century chemists much as had used to isolate the elements po­ Mount Everest challenged twentienth­ tassium and sodium by passing an century mountain climbers. In the I'''/i' electric current through their molten form of several well-characterized '\"~liJ'"'..... , ., .' i hydroxides. But what could he use as . >'" ·f··, ",'."":,' , chemical compounds, fluorine was an electrolyte, since sodium and po­ obviously there, but prior to June 26, tassium fluorides could not be melted 1886, no one had succeeded in isolat­ ;.;~~\~~("F and their aqueous solutions, on elec­ ing the free element from any of its trolysis, produced only hydrogen and compounds-and at least two chem­ oxygen? Davy turned to the noxious ists had died in the attempt. In his fluoric acid, or hydrogen fluoride, a moment of triumph, Henri Moissan low-boiling liquid. "Considerable diffi­ (1852-1907) knew better than anyone culties ensued.... The manner in the debt he owed to those who had which the surrounding atmosphere shown the way up the treacherous became filled with the fumes of fluoric chemical slopes. acid, rendered it, indeed, very difficult As early as 1529, miners and metal to examine.... My fingers became workers noticed a mineral that "by sore beneath the nails, and they pro­ the heat of the fire, like ice in the sun, duced a most painful sensation, [they) liquefy and flow away.... They which lasted for some hours, when are wont to be made use of when they came in contact with eyes." metals are smelted, as they cause the However, Davy was a persistent and material in the fire to be much more at times reckless experimenter, and fluid." The mineral was named fluores he pressed on (see "Nitrous Oxide, from the Latin, fluo, which means "to by No Means a Laughing Matter," flow." Somewhat later, fluores, known Chern Matters, February 1986, p. 17). today as calcium fluoride, was shown Because the hydrogen fluoride at­ to possess two other unusual proper­ tacked glass, he fashioned a small ties. After heating, it glowed in the electrochemical cell from horn silver dark, a phenomenon that later came (a silver chloride mineral) with elec­ to be known as fluorescence. And on trodes of platinum. Alas, his hydrogen treatment with oil of vitriol (concen­ fluoride contained water, and all he trated sulfuric acid), fluores gave rise obtained on electrolysis was a small to a noxious substance that etched amount of hydrogen at the cathode glass, and-as seekers after fluorine and a badly corroded anode. Davy were later to discover-flesh, skin, was forced to give up. and bone, too. Louis-Joseph Gay-Lussac (1778­ The first systematic attempt to liber­ 1850) and Louis-Jacques Thenard ate the element fluorine from its com­ (1777-1857) soon succeeded in ob­ pounds was made by Humphry Davy taining liquid hydrogen fluoride (1778-1829) in the years 1811-1813. largely free of water, only to find that it By then chlorine gas had been made no longer conducted electricity appre­ by Carl Scheele (1742-1786) and had ciably and hence could not be sub­ been shown to be an element by jected to electrolysis! That particular Davy himself. Since fluorine com­ approach to fluorine appeared to be a pounds had many properties similar dead end. to corresponding chlorine com­ Toward the end of his attempts to pounds, it was natural to try first the isolate fluorine, Davy had been forced

13 •

to dismiss William Payne, his "fag recently he had published the quanti­ electricity, but there were very little signs and scrub" (laboratory assistant), for tative laws of electrolysis that now go of any gaseous or vaporous matter being produced ... either there is no decompo­ drunken assault. Previously he had by his name. Having drawn a blank, sition, or else the wire touches the retort, briefly employed Michael Faraday, a as had others before him, with liquid or else fluorine combines or in some ways young bookbinder's apprentice, to hydrogen fluoride, Faraday turned to disappears. assist him while he recovered from the electrolysis of molten lead fluoride He was turned back once more: "I eye and hand injuries suffered in an in platinum vessels. His laboratory cannot go on at present with the fluo­ explosion of nitrogen trichloride. Davy notebook reflects his initial feeling of rine experiments." Faraday was was now able to offer Faraday a per­ success: never again to take up the challenge manent position, though with the Worked for fluorine. There was plenty of of the isolation of fluorine, and it re­ warning "that science was a harsh action. Lead was precipitated on the mained one of the few failures of this mistress, and in a pecuniary point of platina, alloying with it, and gas evolved at most skillful and stubborn of experi­ view but poorly rewarding those who the end of wire P[ositive]; for this gas or menters. At least he lived to tell the devoted themselves to her service." vapor the upper part of the platina tube answered as a receiver. It must have been tale. Others were not so lucky. Faraday was not discouraged, and he fluorine. At the end of his early paper on spent his entire scientific career as a fluorine, the Belgian chemist Paulin grateful and impecunious servant of Several months later, however, we Louyet wrote: the Royal Institution. find the rueful admission: By 1834, when he took up the chal­ I have not obtained fluorine; my expec­ In ending this Memoire, I must point out lenge of fluorine, Faraday was al­ tations, amounting to conviction, passed that it is necessary to take the utmost precautions to avoid the effects of the ready a famous chemist and had away one by one when subject to rigorous examination. vapours of hydrofluoric acid should one begun a series of studies in electricity wish to repeat these experiments; for they and magnetism that would establish The following year Faraday returned act vigorously on animal matter. All chem­ him as the greatest experimental to the attack: ists who have worked with fluorine have physicist of the nineteenth century. In learned this to their cost ... [it produces] Fluorine. Arranged an electrolytic retort needle-like pains under the nails, tempo­ particular he was the master of the thus. Plenty of gas evolved in the Volta rary inflammation of the eyes, chest art and science of electrolysis. Only electrometer, showing the passage of pains, prolonged irritation of the larynx, 14 thick and often bloody sputum, and it passed and no fluorine was pro­ This claim, however, had not stood takes time to recover. Rarely are these duced. The committee charitably the test of time, and artificial dia­ effects instantaneous or rapid. The Rever­ withheld its judgment. Momentarily it monds were not made until the end Thomas Knox almost died; the sick­ ness disappeared only after using hydro­ looked as if fluorine had escaped 1950s. But that is another story. cyanic acid for six months. M. George once again. Moissan quickly proved, Knox felt the effects for three years and however, that some potassium hydro­ had to go to Naples to recuperate. As for gen fluoride (KHF2) needed to be Postscript myself, my health has been profoundly dissolved in the liquid hydrogen fluo­ changed, and I cough blood frequently." Ever since the work of Henri Mois­ ride to provide the necessary electri­ san, chemists have believed that Any malady for which hydrogen cya­ cal conductivity. In his earlier experi­ electricity was essential to the nide (HCN) is the cure is dire in the ment some solid KHF2 had apparently preparation of elemental fluorine. extreme. Alas Louyet did not suffi­ spattered over into the receiver; in his Although it's true that a few exotic ciently heed his own advice, and he careful preparation for the Academy, solids have yielded traces of fluo­ died an agonizing and premature no KHF2 had been present and hence rine on heating, these solids can death. Even so, chemists were still no electrolysis occurred. Moissan be made by using fluorine pre­ willing to continue the assault on fluo­ now deliberately added a small pared electrolytically. As if to salute rine. Jerome Nickles tried and per­ amount of KHF2 to the liquid hydro­ the Moissan centennial, this belief ished in the attempt. Edmund Fremy gen fluoride and quickly had at his has now been shattered. In a short (1814-1894) then took up the chal­ disposal an unlimited supply of pure article to be published in an Octo­ lenge and edged closer to the longed­ fluorine. The committee was recon­ ber issue of Inorganic Chemistry, for summit. In particular, he perfected vened and this time Moissan had his Karl Criste of Rocketdyne Division a method of producing exceedingly triumph. Fluorine had been con­ of Rockwell International describes pure hydrogen fluoride by heating quered at last. a "chemical synthesis of elemental fused potassium bifluoride: Fluorine took its place rather fluorine." Christe first prepares L quickly as far and away the most KHF2(s) - KF(s) + HF(g) potassium hexafluoromanganate reactive of all the elements. Partly (IV) and antimony pentafluoride by In the hands of his student, Henri because of this dangerous reactivity, separate nonelectrolytic methods Moissan, this was to prove the key to it remained primarily of academic from readily available starting ma­ the successful isolation of elemental interest for many years. In the 1920s, terials. fluorine. Thomas Midgley of General Motors It was only after a series of initial showed the value of fluorine-contain­ 2KMn04 + 2KF + 10HF + 3H20 2 failures that Moissan returned to the ing Freons in refrigeration. Somewhat - 2K2MnF6 + 8H20 + 302 time-honored, though previously un­ later, Teflon (polytetrafluoroethylene) and successful, method of the electrolysis was developed by the Du Pont Com­ SbCls + 5HF - SbFs + 5HCI of liquid hydrogen fluoride. He pre­ pany. During World War II, fluorine pared his starting material by Fremy's became central to the preparation of When these two reagents are method. His V-shaped apparatus was uranium hexafluoride, the volatile heated together at 150°C for 1 made of a platinum-iridium alloy, and compound used in the separation of hour, nonelectrolytic "chemical" it was cooled by liqUid methyl chlo­ uranium into the fissionable isotope fluorine is readily obtained. ride. To his delight, and perhaps to his U-235 and the nonfissionable U-238. surprise, he found that on electrolysis More recently, several thousand fluo­ 2K2MnF6 + 4SbFs - a pale yellow gas was produced, at rine-containing compounds have 4KSbF6 + 2MnF3 + F2 the anode, that reacted with normally found uses as pharmaceuticals, in­ unreactive silicon avec eclat to pro­ secticides, high-energy fuels, lubri­ Coming exactly 100 years after duce the known silicon tetrafluoride. cants, and polymers. Moissan's achievement, Christe's Other reactions convinced Moissan The isolation of fluorine was by no chemical isolation of fluorine is a that he had succeeded in isolating the means Henri Moissan's only chemical beautifully timed tour de force. elusive fluorine. achievement. He was the first to build However, Moissan's electrolytic A few days later Moissan was in­ efficient electric furnaces and pio­ process is expected to remain the vited to give a demonstration before a neered the area of high-temperature method of choice for preparing blue-ribbon committee appointed by chemistry. When he received the large amounts of the gas. the French Academy of Sciences. He Nobel Prize for Chemistry in 1906, prepared his liquid hydrogen fluoride this work was cited equally with his with particular care-too carefully, as isolation of fluorine. Toward the end of Derek Davenport is a professor of chem­ it turned out. When Moissan com­ his life he claimed to have made artifi­ istry at Purdue University in West Lafay­ pleted the electrical circuit, no current cial diamonds at high temperature. ette, Ind. 15

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Have you ever wondered how sports­ method is simplicity itself. Open the stone-washed jeans made by his em­ wear manufacturers get that "stone­ box. Remove the Stone from its "bed ployer, Jonbil Inc. After experimenting a washed" look in their blue jeans? Nei­ of denim." Soak your uncool jeans. bit at home, he founded Creative Con­ ther have we. Oh, all right. Here's how Rub the stone all over them for about a cepts of Raleigh, Inc., to market small it works: they open up big industrial week (oh, all right, 15 to 30 minutes). stones to do-it-yourselfers. About washing machines,-toss in 40 poonds Wash and dry them. Remove them, 100,000 pieces have already been sold of jeans and an equal weight in pumice stone-washed. Go outside and make to stores, he says, including The Bon in stones, and then go out to lunch. When fun of your friends. Seattle, Broadway in California, Mar­ they come back, the jeans are nicely Banks got the idea for The Authentic shall Field's in Chicago, the Boston beaten up. Voila! 60 bucks a pair. Stone in May, after discovering a piece Store in Milwaukee and the Milwaukee Needless to say, you kids should not of leftover pumice stone in a pair of Store in Boston. fYVe made that last try this at home. The results will be one up.) Suggested retail price: $6. messy and Mom will be mad. Why not Next to nothing to pay, really, for some­ just invest in The Authentic Stone? If thing that took nature millions and mil­

From Newsweek, Sept. 22, 1986, copyright 1986 Newsweek, Inc. All rights reserved. Reprinted by permission