In sugar refining, molasses is separated from the sugar crystals after each of three boiling or extraction processes that sugar cane goes through. The 3rd and final separation is called blackstrap molasses, and is used mostly as an ingredient in cattle feed.
On January 15, 1919, a large 50 foot high storage tank in Boston burst and sent a tidal wave of over 2 million gallons of molasses traveling at over 30 miles per hour. Houses, buildings and parts of the elevated track system were crushed in its path. Twenty-one people died, and over 150 were injured. It took over 6 months to clean up the mess. The damage was in the millions of dollars.
It is said that you can still smell the molasses on hot humid days in the summer.