Molasses is a fluid of high viscosity that pours quite slowly and that can be expected to move particularly slowly in cold January weather. Any liquid — honey, melted shortening, lava or even water — will move more quickly when hot and move more slowly when cold.
The expression “slow as molasses in January” is an Americanism for someone or something that is painfully slow, and was in use by 1872. It did not arise from the Great Molasses Flood in Boston.
The word “molasses” is derived from the Latin word mel for honey. It’s the dark, sweet, sticky, viscous syrup left over after all the sugary stuff has been squeezed, pressed or boiled out of sugar cane. It was used in the manufacture of ethanol to make weapons in WWI, and of course, in the production of rum. It eventually lost popularity in the US as granulated sugar became cheaper and more available.
The Great Molasses Flood happened on January 15, 1919. It was unusually warm — 43 degrees above zero. But apparently the temperature played no role in what occurred that day in Commercial Street. That’s where a tank filled with 2.5 million gallons of molasses stood, just behind a freight terminal.
Shortly after noon, the tank split wide open, creating a tidal wave of molasses. Men, women, children, and a number of horses were engulfed. High above the scene, an elevated train crowded with passengers whizzed by the crumbling tank just as the molasses broke loose. The flood tore off the entire front of a house and snapped off the steel supports of the elevated train structure. The train had barely gone by when the trestle snapped and the tracks sagged almost to street level.
Fifteen dead were found by that night, and six other bodies were recovered the next day. Many injured were taken to area hospitals.
A small Boston welding company submitted the lowest bid for cutting up the ruptured tank and cleaning up the mess, but the owner deeply regretted winning the job. Not only did he lose money, but the work was a nightmare. Clothes, gloves, torches, hoses — any sort of equipment — were coated with a layer of sticky molasses within minutes of workers being on the job. Inside the broken tank, molasses had crystallized into a 4-inch layer of sugar, which burned with a thick, choking smoke when contacted by acetylene torches. In the spring, flies swarmed to the area, getting inside workers’ helmets and goggles.
The Great Molasses Flood more or less disproved the expression, “Slow as molasses in January.” One of those injured in the disaster was working across the street from the tank when it collapsed. He tried to outrun the wave of molasses to safety, but it caught up with him and he was dragged down into the ooze. So we can assume molasses runs somewhere around 25 to 30 mph in January. Which is not slow.
It was the unlikeliest way to drown. And the true culprit was gravity currents, which come into play when a dense fluid spreads horizontally into a less dense fluid (in this case, molasses into air). The density of the molasses alone would account for the speed of its initial spread.
In the 1941 movie Gone with the Wind, Scarlett O’Hara chides Prissy for being as “slow as molasses in January.” It was an expression that I heard many times as a child, usually applied to me because I seemed to like reading stories better than drying dishes.