Big Bang

On May 5, 1866, a reporter for the New York Times confessed to “some little trepidation” as he headed off to attend a demonstration at a rock quarry. A “professor” would attempt to show that a liquid widely considered to be one of the most dangerous substances on earth was in fact a benign and useful explosive if properly handled. The audience edged backward as the demonstrator poured some of the oily fluid onto a rock and lit it with a match, causing it to “burn like pitch, but not explode.” They cringed as he dropped a vial from a height to show that it would not explode accidentally. When he purposely set off a small quantity of the liquid, all were startled by the “tremendous report.”

The “professor” was Alfred Nobel. The 33-year-old Swedish engineer was promoting what the reporter described as “that cheerful compound ordinarily recognized as nitro-glycerine.” Nobel had begun to ship this “blasting oil” two years earlier. It was the first new commercial explosive since engineers had begun to use traditional gunpowder in mines in the seventeenth century. Orders had poured in from all over the world. America was the most promising market of all; breakneck industrial growth, especially the spread of railroads, had created an urgent need for an explosive that could muscle through hard rock.

The nervousness of those attending the demonstration was understandable. They knew that the previous November a salesman’s sample of nitroglycerin had blown up outside a Greenwich Village hotel, injuring 18 people and leaving a four-foot crater in the pavement. By one account, “Every window was shattered, the doors of the stores and dwellings broken open and the chimneys thrown down.” They were aware that in April a shipment to the California goldfields had exploded while workers were unloading it in Panama. That blast had killed 60 and wrecked half a million dollars’ worth of property. The Times called it “one of the most terrible accidents on record.” A few days later another shipment had destroyed a San Francisco Wells Fargo office, smashing windows for half a mile, a newspaper reported, and throwing a human arm against “a third story window of the building across the street.”

An alarmed Congress was considering legislation to restrict shipment of the dangerous material and to make any accident involving nitroglycerin a criminal, perhaps even capital, offense. Railroads and steamship lines were refusing to take it as freight; possession was as good as outlawed in Britain, France, and Belgium. Nobel, his name reviled around the world, had been asked to leave the New York hotel where he was staying and to take his nitroglycerin samples with him. As he scrambled to salvage his business, he received word that his own factory near Hamburg, Germany, had blown up.

The high-explosives industry, which would prove to be one of the most influential technical catalysts of modern times, was off to a shaky start.

Nitroglycerin had been discovered in 1847 by an obscure Italian chemist named Ascanio Sobrero. He had been treating organic compounds with nitric acid, hoping to discover new dyes and medicines. He found that he could make the acid react with glycerin, a sweet, syrupy byproduct of soapmaking, but only if he trickled in the glycerin very slowly, kept the mixture cool, and added strong sulfuric acid. Then he realized that the resulting oil, once separated from the acids, was the most powerful explosive ever created. A trace of it deposited on an anvil and struck with a hammer set off a window-shaking concussion.

A drop was heated in a test tube,” he reported, “and exploded with such violence that the glass splinters cut deep into my face and hands, and hurt other people who were some distance off in the room.” He judged the material, which he called pyroglycerine, too dangerous to manufacture. It was likely to remain a useless curiosity.

Not only was the chemical remarkably explosive, he noted, but a drop of it on his tongue produced a violent headache. Through the 1850s researchers in homeopathy would prescribe a dilute form of nitroglycerin, which they called glonoin oil, for headaches, on the principle of “like cures like.” Medical investigators later found the chemical to be an effective remedy for angina pectoris, for which it is still prescribed today.

During the early 1860s Nobel, inspired by his father’s experiments with explosives, began to look for a means to turn nitro into a useful blasting agent. He found a way to manufacture it with relative safety but then faced another problem. Gunpowder had always been set off by a burning fuse, but fire would not usually ignite nitroglycerin. How could he detonate the material reliably?

In 1863 he hit on the idea of using a lesser explosion to shock the nitro into detonation. “I therefore lay claim to the idea so far as industrial use is concerned,” he wrote in his patent application, “of contriving by administering a mere initial impulse to develop an explosion in substances which, exposed, can be brought into contact with burning bodies without exploding.” The idea of an initiator, one explosive setting off another, was the stroke of genius on which the entire field of high explosives was founded.

At first Nobel used black powder (traditional gunpowder) as the initiator. He placed a small container of it inside a charge of nitroglycerin and exploded it with an ordinary fuse. Later he switched to the more efficient mercury fulminate, which an engineer could detonate with either a fuse or an electric spark. The initiator was a kind of kindling, an easily detonated intermediary between the spark or match and the nitroglycerin.

Nitroglycerin’s innate sensitivity remained a vexing problem, as did the fact that unless it was absolutely pure, it was subject to unpredictable decomposition and spontaneous explosion. Shipping, which subjected the liquid to jolting and leakage, was a particular hazard.

Nobel, though shaken by the series of disasters, was aware of the urgent need for an explosive more powerful than black powder for mining and public works projects. He hurried back to Europe to try to salvage his business.

Americans were not content to wait. Mighty works were afoot, and if they required risk, so be it. One man who defied public apprehension was George Mowbray, an English immigrant trained as a druggist who had traveled to Titusville, Pennsylvania, after Edwin Drake drilled the first oil well there in 1859. Mowbray operated a refinery for a few years, then turned his attention to nitroglycerin.

Oilmen had discovered that they could rejuvenate slow-flowing or exhausted wells by detonating explosives inside, fracturing nearby rock. In 1865 Edward A. L. Roberts used a “torpedo” containing eight pounds of black powder for the job. Two years later he switched to liquid nitroglycerin, which gave much better results. He bought from Nobel’s American licensees the exclusive rights to use nitro in oil wells.

The business of well “shooting” became a contentious one as drillers tried to avoid the hefty fees—up to $1,300 per well—that the Roberts monopoly charged. Moonlighters started brewing nitroglycerin in out-of-the-way shacks. Since their blasts shot telltale geysers of water or gravel high into the air, they used the cover of darkness to avoid the Pinkerton detectives Roberts hired to enforce his rights.

Of course, accidents accompanied this activity. Roberts’s own factory was completely demolished in an explosion, leaving a hole reported to be “large enough to contain a dwelling house.” Men were often “blown to atoms,” leaving remains that would barely fill a cigar box. “Nitroglycerine literally tears its victims into shreds,” a contemporary historian wrote. “It is quick as lightning and can’t be dodged.” But while the accidents served as grim warnings, they also graphically illustrated the extraordinary power of high explosives, further boosting demand.

Mowbray left the oil fields in 1867 and at 53 took his process for making nitroglycerin to northwest Massachusetts. There he signed on with one of the most ambitious railway projects of the day. Engineers were boring into Hoosac Mountain with an eye to completing a tunnel almost 5 miles long and 22 feet high. When finished, it would connect Boston to the burgeoning economy of the West. But workers had been digging off and on since 1851 and so far had penetrated barely a mile into the mountain. The resistance of granite to black-powder blasting had hampered the work and inflated the cost of what was ridiculed as the “Great Bore.”

Knowing the difficulties of transporting nitroglycerin, Mowbray set up his factory right at the western portal of the tunnel. There he became the first American to manufacture nitroglycerin on a commercial scale. A careful chemist, he devised an efficient and relatively safe method that involved dripping glycerin from glass jars into 116 stone pitchers of acid that he set in ice-water troughs. He pumped cold compressed air into the pitchers to stir the ingredients. When the process was complete, workers poured the mixture into a large vat of water, where the insoluble nitroglycerin settled out. They drew it off and washed it several times with fresh water to remove traces of acid. The result was a 450-pound batch of fluid, “the color and consistency of olive oil,” as a chemist described it. With this simple apparatus, Mowbray eventually produced more than a million pounds of nitro-glycerin, which he used at Hoosac and sold across the country.

Workers carried the nitroglycerin—some 6,000 pounds of it a month—into the tunnel and inserted canisters of it into the drilled holes. Blasters set off the liquid by sending a charge of static electricity down wires insulated with gutta-percha. Equipped with the new explosive, which was generally considered to be ten times as powerful as black powder, the tunnelers chewed through the mountain at an accelerated rate. Progress doubled to 51 feet a month. The tunnel was finally completed in 1875, having cost $9.2 million and the lives of 200 workers. It was the longest rail tunnel in America at the time and one of the great engineering feats of the century.

Mowbray knew that nitroglycerin froze at around 50 degrees Fahrenheit, and it was generally believed that frozen nitro was far more sensitive to shock than liquid. During the harsh winter of 1867–68, canisters of the explosive were needed to unblock an ice dam on the other side of the mountain. Mowbray packed them in warm sawdust and threw a buffalo robe over the cargo before sending C. P. Granger, an engineer, to make the delivery. Descending the mountain in deep snow, Granger’s sleigh overturned. By the time he reassembled the nitroglycerin, he found it had frozen solid. According to Mowbray, he “proceeded on his way, thinking a heap but saying nothing.” When he arrived, he found that a blasting cap could not detonate the frozen canisters. The nitro became effective again only after it thawed.

The discovery was a boon to Mowbray’s business. From then on, he stored and shipped nitroglycerin frozen. He devised special railcars to carry it packed in ice, an attendant always on hand to monitor the temperature. In 1877 he sent 100,000 pounds of nitroglycerin all the way to Manitoba for railroad blasting. The shipment traveled by train, boat, two-wheeled bull cart, and finally on men’s backs, all without incident.

Other daredevil manufacturers, some with little knowledge of chemistry, were traveling the country during the 1870s setting up nitroglycerin factories—often little more than makeshift sheds—near work sites where the explosives were needed. Engineers used liquid nitro extensively to drive the Central Pacific rail line through the Sierra Nevada, cutting months and millions of dollars from the job. Mowbray always insisted that his “tri-nitro-glycerine” was different from Nobel’s patented blasting oil, but they were the same substance (the more formal chemical name is glyceryl trinitrate). Eventually the American patent holders sued Mowbray and forced him to give up the trade.

Any chemical explosion involves a sudden conversion of a solid or liquid into a much larger volume of gas. The gas, confined within the same space as the original material and heated to extremes by the energy of the reaction, exerts pressure on whatever surrounds it. This pressure, moving outward in a shock wave, can bend and fracture rock, move earth, or demolish a building.

Black powder, a physical mixture of sulfur and charcoal with potassium nitrate, explodes through rapid combustion, a chain reaction of fire racing through the powder as the decomposing nitrate gushes oxygen. It is designated a low explosive. In high explosives, the oxygen is contained inside the very molecule itself, along with its fuel. Detonation is propagated not by fire but by a shock wave that spreads through the material at supersonic speed, shaking apart each molecule and setting off the whole mass almost instantaneously.

The temperature of a nitroglycerin explosion instantly reaches 3,500 degrees centigrade, equal to the melting point of a diamond. The hot gases generate a phenomenal pressure, throwing out a shock wave in all directions at a speed of 17,000 miles an hour (about eight times as fast as a rifle bullet). Describing the difference between a black-powder blast and the detonation of nitroglycerin, the historian G. I. Brown wrote, “It is the difference between being bumped into by a pedal cyclist or being knocked for six by an express train.”

Speed is everything. A slice of cheesecake contains more calories of potential energy than an equal portion of nitroglycerin. But while the weight watcher spends an hour or two in the gym working off a dietary indulgence, the explosive releases all its energy with a suddenness that defies imagination—barely a millionth of a second.

In spite of the success of Mowbray and others at putting pure nitro-glycerin to work, the liquid’s drawbacks and dangers remained. Alfred Nobel, in his second and more famous insight, found a way to use and transport the volatile explosive safely. He absorbed the oil in a diatomaceous earth known as kieselguhr, which could hold three times its own weight in nitroglycerin. He packed the resulting puttylike substance into tubes and exploded it with the detonators he’d already invented. Though not quite as powerful as pure nitroglycerin, it was much safer and more convenient. He referred to the new product as Nobel’s Safety Powder or by its more common name, dynamite.

Patented in America in 1868, dynamite was one of the most successful products ever to hit the market. Nobel’s factories produced 11 tons of it in their first year of operation, 185 tons three years later, and by 1874 were turning out more than 3,000 tons annually. So sought after was the product that Nobel immediately began to struggle with a horde of imitators bent on marketing their own versions, patent or no patent.

“In the Old World,” his biographer Herta Pauli wrote, “the story of high explosives would be one of inventions, high finance, power politics, and wars. In the New World, it started as one of patents, petty swindles, litigation, and accidents.”

Nobel licensed his American rights to a California firm called the Giant Powder Company ( powder continued as a general term for explosives even though most of the new compounds were not powders). The company set off the first dynamite in the United States in 1867. Hard-rock miners and railroad builders in the West eagerly embraced this more practical explosive. In the East, gunpowder makers like the du Pont family staunchly resisted the rival product. Mineworkers imagined that because of its effectiveness, dynamite could endanger their jobs. They sometimes threatened dynamite salesmen with violence.

Nobel’s original product, known as “guhr dynamite,” was not used for long in the United States. American chemists tried to circumvent his patents by devising different ways to absorb nitroglycerin. Instead of diluting it with inert clay, they saturated chemicals that could themselves contribute explosive power to the reaction. These “active dope” products proved more powerful and more cost-effective than Nobel’s invention. Known as “straight dynamite,” they quickly came to dominate the U.S. market.

Some of the credit for their early development belongs to James Howden, a chemist who had blasted rock with pure nitroglycerin for the Central Pacific line. The California Powder Works, a West Coast gunpowder company, hired Howden to come up with a new product when they found that Nobel’s Giant Powder was eating into their market. In 1872 he devised a nitroglycerin-based explosive that used potassium nitrate, sugar, and other chemicals to absorb the oil. He called the new product Hercules Powder.

The battle was joined, and dynamite formulas quickly began to proliferate. Talliaferro P. Shaffner devised Porifera Nitroleum by adding nitroglycerin to ground sponge, cotton fiber, and sawdust treated with sodium nitrate. Vigorite, another popular explosive, was a composition of nitroglycerin with potassium chlorate, charcoal, dextrin, and sumac. An English inventor named John Horsley created a patented explosive by combining 4 parts nitroglycerin with some potassium chlorate and 16 parts gall apples.

Nobel, indefatigable, soon made his own breakthrough, his third major contribution to explosives technology. In 1875, instead of saturating an absorbent with nitroglycerin, he dissolved it in nitrocellulose. The result was a gelatin that not only was waterproof but was even more powerful than nitroglycerin alone and ideal for hard-rock blasting.

Although engineers welcomed explosives with greater shattering power—“brisance” they called it—they also saw that for many jobs, especially moving earth, they needed a slower, heaving explosion. “Between black powder and Nobel’s dynamite there was a great gap to be filled,” a publication of the California Powder Works noted. To fill the gap, Egbert Judson patented Judson Powder, which contained potassium nitrate and sulfur along with anthracite coal and asphaltum mixed with only 5 percent nitroglycerin. Many similar mixtures joined the ranks of “graded” dynamites.

Hercules, Neptune, Ajax, Vulcan, Samson—explosives makers scoured mythology to tout the potency of their products. At first they avoided Nobel’s term, but before long the word dynamite had become generic. Patent suits flew with a frequency that warmed the hearts of lawyers but had little long-term effect on the industry, which continued to expand at an unprecedented pace through the rest of the nineteenth century. With the expiration of the original patents in the 1880s, the price of the product fell from $1.75 to less than 50 cents a pound.

After warning for several years of the dire peril of high explosives, black-powder makers reversed course and began making dynamite themselves. Their marketing and technical clout allowed them to jump into the business with both feet. In 1880 the du Ponts and a consortium of other powder makers started a dynamite factory in Repauno, New Jersey. It soon became the largest plant in the world, and by the turn of the century the DuPont company controlled much of the explosives industry in America.

Though marked by the occasional horrific accident, the business became relatively safe. In the early days workers tending the nitrification process sat on one-legged stools, lest they doze off and let the reaction get out of control. Because of their exposure to nitroglycerin, they suffered from intense headaches when they first started on the job. After about two weeks they became acclimated, and the pain subsided. In order to avoid a recurrence of “NG head” after a time away from the factory, workers sometimes took vials of nitroglycerin with them on vacation and consumed minute amounts to maintain their tolerance.

We think of dynamite explosions as spectacular events, but they actually tend to be invisible. Engineers prefer to place charges so that they perform useful work rather than send debris flying, and a blast is over in an instant. So it’s easy to forget the role these potent chemicals have played in shaping our world. Their invention helped bring about, in the late nineteenth and early twentieth centuries, a heroic age of engineering.

Transportation was among the first beneficiaries of the new technology. Before high explosives, travel in the United States was far more difficult. Mountains presented formidable obstacles to rail lines; rivers and ports were often obstructed; roads remained primitive. Explosives vastly speeded the digging of tunnels for trains and the clearing of shipping channels. They economically shattered the rock needed for roadbeds. Concrete highways required nearly a ton of explosives per mile.

High explosives made possible public works on a scale never before imagined. New York’s New Croton reservoir system, completed in 1890, was carved with 7 million pounds of dynamite. The excavations for the foundations of the city’s proliferating skyscrapers were shaped by dynamite. Its subway system, begun in 1900, gobbled up another 10 million pounds of explosives.

Progress on the Panama Canal, the most monumental engineering project of the time, was speeded by use of more than 61 million pounds of high explosives. One of the largest blasts occurred in 1913, when President Woodrow Wilson pushed a button to fire 80,000 pounds of dynamite and open the dike that made the waterway continuous across the isthmus.

Production of coal in the United States grew from 14 million tons in 1860 to more than 500 million tons in 1910, and high explosives did much of the heavy lifting. The mining of ore for iron, steel, copper, and aluminum likewise benefited. The first Portland cement mill in the United States opened in 1871, and the concrete industry grew in parallel with the high explosives that made its raw materials affordable. Ten million pounds of dynamite went into the construction of Hoover Dam, and Gutzon Borglum used 6,000 pounds of it to blast the rough shape of George Washington’s face from Mount Rushmore.

So eager were dynamite manufacturers to sell their product during the early twentieth century that they even promoted it to farmers as an all-purpose tool. Customers could blast stumps or disintegrate boulders. They could blow open ditches for drainage and loosen the soil before planting fruit orchards. Farmers often built isolated “dynamite houses” where they could store the explosive.

Though most of the early high explosives were based on nitroglycerin, other formulations appeared. In 1871 the English inventor Hermann Sprengel proposed using separate oxidizing and combustible substances and mixing them together just before use. This would overcome the cost and danger of transporting materials that could explode accidentally.

The idea was picked up in America, where Silas R. Divine patented an explosive in 1881 that he called Rack-a-rock. It consisted of paper or cloth bags of potassium chlorate soaked with nitrobenzene shortly before use, then packed in sealed copper cartridges. The most spectacular use of Divine’s invention came four years later, when engineers used it to pulverize Flood Rock, a barely visible but exceedingly treacherous obstacle in Hell Gate Channel, which connects New York’s East River with Long Island Sound. Rocky ledges and unpredictable currents had brought ships to ruin there for generations.

Gen. John Newton of the Army Corps of Engineers directed that water be held back from Flood Rock with cofferdams while shafts were driven 70 feet into it. Miners worked for nine years honeycombing the rock with galleries, which they charged with 240,000 pounds of Rack-a-rock and 42,000 pounds of dynamite. The explosion of the dynamite was to act as an initiator and set off the less sensitive Rack-a-rock.

If it worked, it would be the most powerful man-made explosion ever to occur on earth. On the morning of October 10, 1885, some 50,000 New Yorkers lined the shore and crowded onto rooftops to watch. Newton’s 12-year-old daughter, Mary, pushed a button to set off an electric detonator. Onlookers heard “a deep rumble, then a dull boom.” The ground gave a sickening shake. Then, across nine acres of river, a mass of water and debris sprang up, at points reaching 200 feet into the air. Flood Rock was reduced to fragments. When the dredgers finished, the channel’s perils were, The New York Times said, “smoothed into an inviting smile.”

High explosives are like the genie that, released from its lamp, can work both good and evil. The first decade of the twenty-first century, with its suicide bombs and improvised explosive devices, bears testimony to the destructive potential of high explosives when used with malevolence. But the impulse is hardly a new one. What were known as dynamite “outrages” began soon after its invention.

Whereas black powder was bulky and required a substantial milling operation to make, nitroglycerin was compact and could be mixed up in a home laboratory from readily available ingredients. Revolutionaries saw dynamite as the artillery of the proletariat, a weapon that would allow workers to stand up to the guns of the ruling class. As gunpowder had brought down feudalism, they reasoned, dynamite would topple capitalism. In 1881 Russian revolutionaries managed to assassinate Czar Alexander II with a dynamite bomb after seven unsuccessful attempts. Irish Fenians soon kicked off their own dynamite campaign against their English oppressors.

In america the decade of the 1880s was upset by enormous economic inequalities, a flood of immigrants, and the colliding aspirations of capital and labor. In response, some revolutionaries adopted an almost mystical notion that explosives could demolish intractable social conflict and bring on a new age. Among them was Johann Most, a one-time bookbinder and actor who had grown up in wrenching poverty and immigrated to America from Germany in 1882. Having accepted the seductive notion that “against tyrants all means are justified,” Most became fixated on one means. “Chemistry will liberate the laborer,” he declared. “To be sure of success, revolutionaries should always have on hand adequate quantities of nitroglycerine, dynamite, hand grenades, and blasting charges.” Others took up the chant. “Dynamite is the emancipator,” revolutionary publications proclaimed. “Hurrah for dynamite!” Most took a job at a New Jersey dynamite factory in order to learn the details of its manufacture. He published The Science of Revolutionary Warfare , which was sold at anarchist picnics. “In giving dynamite to the downtrodden millions of the globe,” another anarchist wrote, “science has done its best work.”

On May 3, 1886, a lockout at Chicago’s McCormick Reaper works turned violent, and two unionists were killed. Labor leaders called a protest rally for the next night in Haymarket Square. Three thousand sympathizers showed up, but with rain threatening, the crowd dwindled to a few hundred. As the event was winding down, a force of about 180 policemen appeared and ordered the radicals to disperse. A dynamite bomb suddenly sailed through the air and exploded among the police. Chaos followed, with police firing revolvers indiscriminately into the crowd in what a Chicago Herald reporter described as a scene of “wild carnage.”

Seven policemen died, along with an uncounted number of citizens. The ensuing reaction, America’s first Red scare, resulted in the death penalty for seven anarchist leaders, several of whom had not even attended the rally. Revolutionaries like Johann Most, sobered by the experience, began to back away from their enthusiasm for dynamite as a political cure-all. Explosions occasionally punctuated Western labor disputes during the late nineteenth and early twentieth centuries, but they never became commonplace in this country.

Military men, on the other hand, were naturally and continually interested in the potential of high explosives. They had used black powder in mines and artillery shells during the Civil War, but advanced fortifications and increasingly heavy armor on battleships neutralized much of its power. Dynamite, they thought, could be more potent if hurled against an enemy’s defenses. The problem was that the shock of being fired from a gun was itself enough to set off the nitroglycerin before it left the muzzle.

During the 1880s the military turned to dynamite guns that used the gentler force of air pressure to loft a shell a mile or more. Their compressors, reservoirs, and valves made the weapons bulky, though coastal guns that fired 600-pound dynamite shells were installed in New Jersey. The Navy built a ship called the Vesuvius that managed to fire a few dynamite shells during the Spanish-American War, but with little effect. The idea was soon abandoned.

Other chemicals, not quite so explosive as nitroglycerin but better suited for military uses, were already being developed. Engineers had to satisfy a laundry list of requirements for a military explosive. It had to be cheap, based on readily available raw materials, safe to handle, not easily detonated by impact yet powerful when it did go off, stable, noncorrosive, nontoxic, and easily melted so that it could be poured into shells.

French researchers found a partial solution in trinitrophenol, which had long been known as picric acid. They loaded it into shells as early as 1885. But picric acid was corrosive to metals and had other drawbacks. By the turn of the century German scientists had developed trinitrotoluene (TNT). That substance was based on an organic chemical, toluene, that they were able to extract from coal tar. Soon TNT, more stable and less corrosive than picric acid, though not as powerful as nitroglycerin, became the most widely used military explosive. Scientists came to regard it as a standard for all explosives, even measuring the power of the atomic bomb in terms of equivalent tons of TNT. During the bombardments of World War I, TNT-filled shells rained an unprecedented hell on front-line troops.

On a spring morning in April 1947 longshoremen were loading fertilizer onto a ship in the port of Texas City, Texas, when a blaze broke out onboard. While the fire brigade struggled with the flames, the ship’s cargo exploded. The blast, the worst industrial accident in the nation’s history, killed 560 people and injured 3,000 more.

The incident put a spotlight on a chemical that was to take on an important role in making the explosives industry safer and more efficient—ammonium nitrate. Not at all sensitive alone, ammonium nitrate can become a vigorous explosive when mixed with fuels like petroleum, carbon, or powdered aluminum.

Two Swedish inventors had patented the mixture of ammonium nitrate and carbon as an explosive as far back as 1867. Alfred Nobel had used the salt during the 1870s to create “extra” dynamite. Engineers had included it in what were called “permissible” explosives for use in coal mines. Because they exploded at a relatively low temperature, these blasting agents were less likely to ignite the dust and methane that collected in mines. Ammonium nitrate had also been mixed with TNT during World War I to yield the potent explosive amatol.

During the 1950s commercial blasters turned to mixtures of ammonium nitrate with about 6 percent fuel oil, a product known as ANFO. Like Sprengel explosives, the substance could be mixed at the site of the blast. Because it required a hefty shock to detonate, engineers carried Nobel’s detonator principle one step further: They used an easily exploded blasting cap to set off a booster charge. The booster, an explosive of medium sensitivity, gave enough of a bang to cause the ANFO to explode. The terrorist Timothy McVeigh took advantage of the technology to create the four-ton bomb that did such deadly damage in Oklahoma City in 1995.

ANFO and other explosives, collectively known as “blasting agents,” were safer and cheaper than dynamite and more effective for most earthmoving duties. They largely replaced nitroglycerin-based agents during the second half of the twentieth century. In 1957 dynamite still constituted 95 percent of the explosives used in the United States; today it amounts to less than 2 percent. So thoroughly did the new explosives take over that in 1974 DuPont, long the premier high-explosives maker in America, announced that it was phasing out its production of dynamite.

Explosives are still one of our most ubiquitous forms of chemical technology, and they still remain largely hidden. Every hour, around the clock, engineers detonate an average of 628,000 pounds of high explosives in the United States—5.5 billion pounds annually. About two-thirds of that is used in the coal industry, with mining of metal ores and quarrying accounting for much of the rest. A wide range of different types of explosives are used for other applications, from seismic exploration and firefighting to welding, demolition, and logging.

Alfred Nobel was a gloomy idealist. He warned in 1892 of “a new reign of terror … one seems to hear its hollow rumble in the distance al-ready.” Yet he remained rightly convinced that explosives were, in the final reckoning, a boon to humanity and a pivotal contribution to the formation of our modern world. His relatively simple inventions, the blasting cap and dynamite, together with his acute business sense, allowed him to amass untold wealth. At his death, in 1896 at age 63, he left his fortune to prizes for those who advanced the cause of peace or who made important contributions to the sciences and the arts. The world takes explosives so much for granted today that Nobel is much better known for those prizes than for his world-changing inventions.