The box, stored in the back room among the unclaimed freight, appeared to be leaking. Haven and Webster, the freight clerks sent to check it out, arrived with tools to pry open the crate. The ensuing blast shattered every window on the street, including some a half mile away, killing the two men and 13 others at work in surrounding buildings.
It was April of 1866, and the box, stored in the San Francisco office of Wells, Fargo & Co., was full of a liquid called “Nobel’s Blasting Oil,” which the Placer Herald of Auburn, California described, in a graphic news brief about the incident, as “a new explosive five times more powerful in its effects than [gun]powder.”
They weren’t the first deaths caused by the combustible liquid branded with Alfred Nobel’s name. Just two years earlier, the Swedish inventor’s younger brother, Emil, was killed in an explosion at the family factory in Stockholm. Explosives had become a vital tool of industry, used to mine everything from silver to salt, but blasting oil was volatile, and accidental detonations weren’t uncommon.
It was a deadly problem, but a year after the explosion in downtown San Francisco, Nobel had a solution. By mixing the oil with a stabilizing agent, he created the safest, most controllable explosive the world had ever seen. It was a divisive invention – years later, a French newspaper would credit Nobel with “finding ways to kill more people faster than ever before” – but one that has shaped society and helped extend the bounds of what humans can build: dynamite.
For nearly 1,000 years, the only widely-used explosive was black powder. A mixture of sulphur, charcoal, and potassium nitrate, black powder is what’s called a low explosive: it deflagrates, or burns, creating heat and gas. When that reaction is contained, it produces explosive energy – enough to propel a bullet from a gun (but not enough to burst the barrel), and, in high enough quantities, enough to blow through rock. In mining and engineering, powder was a passable, if imprecise, tool.
Then, in 1847, an Italian chemist named Ascanio Sobrero mixed glycerol with nitric and sulphuric acids, and created the first high explosive. Nitroglycerin doesn’t deflagrate: it detonates. When the molecular bonds between the liquid’s carbon, nitrogen, hydrogen and oxygen break, the molecules rearrange into gasses like dinitrogen and carbon monoxide. That kicks off a chain reaction that charges through the fuel, sending out a white-hot, supersonic wave with an explosive energy many times that of black powder. Any bump or jolt can trigger the reaction, making nitroglycerin incredibly unstable, to the extent that Sobrero didn’t believe his discovery had any practical uses.