The Magical Chemistry Behind Smith’s Ice Melt

The night before a snowstorm, as students across campus hunker down with hot chocolate and cross their fingers for a snow day, Smith Facilities Management gets to work. They roll out trucks pouring a sticky, sometimes smelly, brown substance onto Smith’s roads and walkways. This mysterious concoction is called Liquid Magic, and its contents have much to reveal about the science behind ice melts.

The term ice melt is a bit of a misnomer; most ice melts actually work by preventing water from freezing in the first place. Water molecules in liquid water are in constant motion. As temperatures lower, they move more slowly and form hydrogen bonds with each other, freezing at 32°F when these hydrogen bonds lock them into an ordered crystalline structure.

Ice melts, such as the commonly used sodium chloride (NaCl) rock salt, make use of a phenomenon called freezing point depression. When NaCl dissolves in water, it dissociates into its individual ions, Na⁺ and Cl^-. These ions get in between water molecules, disrupting their ability to hydrogen bond with each other. In order for water molecules to overcome the disruptions and form the crystalline structure of ice, the temperature needs to be lower than 32°F. Rock salt can lower the freezing temperature of water to -6°F.

While Facilities Management puts down rock salt for traction after a storm, Liquid Magic, which they spray on dry ground before a storm, does not contain NaCl. Instead, it is 50% magnesium chloride, a different type of salt, and 50% Distilled Condensed Solubles (DCS). This mixture is supposed to be more effective at lower temperatures than regular rock salt. Pretreating the ground with it before a storm makes plowing easier the next day by creating a barrier between the freezing water and the pavement as temperatures drop overnight. “I have used this for probably 25 years…makes my life a lot easier, and your safety–that's why we're doing it,” said John LaBrie, the Grounds Manager at Smith College.

Magnesium chloride (MgCl₂) and calcium chloride (CaCl₂) are the salts that most cities and institutions conducting large-scale salting operations use. The freezing point of a solution is a colligative property, which means that it changes with the amount of solute, or dissolved particles, in the solution. When MgCl₂ or CaCl₂ dissolves in water, they dissociate into three particles, as opposed to NaCl’s two particles. This increases the ratio of solute to water, allowing them to lower the freezing point of water even more than regular salt can.

The bulk of Liquid Magic’s anti-icing capability, though, comes from the DCS. DCS is waste from the distilling industry, specifically the purification of vodka or rum, and it contains a variety of sugars and other small carbohydrates. These molecules disrupt hydrogen bonds just like salt ions do. However, carbohydrates are nearly ten times more soluble in water than salt is, meaning that water can hold many more carbohydrates in solution than salt ions, so DCS results in a much higher ratio of solute to water. This enables Liquid Magic to bring water’s freezing point to -45°F.

In addition to Liquid Magic’s ability to prevent ice at lower temperatures than salt, the desire to reduce the amount of chloride (Cl^-) around campus factors into Facilities Management's use of Liquid Magic. The chloride ions from salts kill grass and degrade the concrete in catch basins around campus. They are also highly toxic to aquatic organisms when they accumulate in bodies of water. “Everything the town puts down as well goes down into [Paradise Pond] and out to the river, so we try not to use rock salt like a first resort,” LaBrie said. Many cities and institutions are now opting for non-toxic, biodegradable carbohydrate-based ice melts like DCS to avoid the environmental concerns of rock salt. Molasses and beet juice are popular options.

Paradise pond in the snow. By Ada Fiala.

“We now have a snow consortium together with Amherst, UMass, Mount Holyoke, and Hampshire. So we kind of meet before the storms, and we have monthly meetings about winter, and everybody discusses what they use,” LaBrie said. Chemistry and careful planning are the foundation of ice melt magic.

By Ada Fiala