Shortly after noon on Jan. 15, 1919, Boston’s North End was shaken by the bursting of a giant iron tank atop the Purity Distilling Co. on Commercial Street. When the 50-foot tank ruptured, an estimated 2.3 million gallons of molasses flooded the streets, killing 21 people and injuring about 150 more.
Science writer Ferris Jabr takes a look at the scientific qualities of molasses in this month’s issue of Scientific American, endeavoring to answer why the flood of brown, goopy sweetener proved far more destructive than a flood of water would have.
“To fully understand this bizarre disaster, we need to examine what makes it unique — its very substance,” Jabr wrote in the article, posted to the magazine’s website.
Unlike water, molasses is a non-Newtonian fluid, meaning that its viscosity, or thickness, changes based on the outside forces that are applied. For example, if a non-Newtonian fluid like yogurt is shaken or stirred rapidly, it becomes thinner and can be poured from a container.
“Consider non-Newtonian fluids such as toothpaste, ketchup, and whipped cream,” Jabr wrote. “In a stationary bottle, these fluids are thick and goopy and do not shift much if you tilt the container this way and that. When you squeeze or smack the bottle, however, applying stress . . .
An explosion, probably caused by a buildup of carbon dioxide inside the tank, burst the tank’s rivets with the sound of gunfire and propelled the molasses into the streets of the North End.
“In the beginning, the molasses was moving so quickly and there was so much of it that it had enough force to rip buildings apart,” Jabr said in a phone interview. “As it went on, it slowed down and became more and more viscous.”
Within seconds of the initial deluge, two full city blocks were submerged. People on the street were crushed by the massive wave. A large section of the elevated train tracks nearby collapsed. Horses were carried off to their demise or were shot to end their suffering. At least one man was swept away and dropped in Boston Harbor.
“Men and women, their feet trapped by the sticky mass, slipped and fell and were suffocated,” the Globe reported in a 1968 retrospective. “The stronger tried to save others, and many of them died for their heroism.”
Trying to swim through the molasses would have been futile; anyone trapped in the gelatinous molasses “would stay in place, like a gnat trapped in tree sap,” Jabr wrote.
The faulty tank was used to facilitate the transfer of molasses between ships in Boston Harbor and railroad tank cars and had already raised concerns among residents.
“The tank went up in 1915, and people started complaining that it was leaking. They could see brown streaks coming out from around the rivets,” said Robert J. Allison, chairman of the history department at Suffolk University. “So the company’s response was to paint it all brown.”
The lasting impact of the flood, in addition to the weeks of cleanup and a massive class-action lawsuit, was mandatory inspections of similar tanks, Allison said.
Now, he said, many people think of the flood as a funny anecdote in Boston history.Colin A. Young can be reached at firstname.lastname@example.org or on Twitter @ColinAYoung.