If you live anywhere in the midwest, then you are accustomed to salt and brine coating your car this time of year. In fact, on some days, you are probably praying for rain just so your car can look decently clean.

Everyone knows that the department of transportation uses salt during winter weather events to melt the snow/ice. However, do you know what it is about salt that actually melts the ice? Well, you are going to learn the science and the history about the use of salt during snow events.

The scientific term for table salt is sodium chloride and the chemical formula is NaCl (Na is sodium and Cl is chloride). Salt is an essential compound used on an every day basis. We salt our food with it, we salt our pools with it and we even gargle salt water when we have a cold. Salt also has ancient history. It was used thousands of years before Christ to preserve food for later consumption.

We first need to understand exactly what the process of freezing is before understanding the impact salt has on snow and ice.

Gas and liquids are considered “fluids” in which the atoms of a compound flow freely throughout the substance. In this case, we are talking about water which is composed of two hydrogen atoms and an oxygen atom (H2O for short).

Image courtesy of NASA

When a liquid freezes into a solid, the atoms form a tightly packed and rigid structure that holds its shape and keeps a fixed volume. This is the reason for the solid appearance of ice compared to liquid water.

When salt dissolves into water, the sodium and chlorine atoms separate and act to prevent water molecules from forming into a rigid structure and therefore prevent ice from forming at temperatures below freezing.

Visual representation of how salt prevents water from freezing into ice. Image courtesy of the USGA.

Now, you might have heard that typical salt loses its ice melting effectiveness at colder temperatures and this is correct. Salt is not very effective at melting snow/ice at temperatures less than 15°F. When the temperature is colder than 15°F, the department of transportation opts to use either magnesium chloride (MgCl2) or calcium chloride (CaCl2) which feature more ions that assist in melting the ice.

What is the history of using salt to melt ice?

Interestingly, the history of using salt to treat wintry roads is not all that old, especially when compared to the history of other salt uses. In the early 1940s, the state government of New Hampshire began to use salt as an experimental treatment for icy roads.

Obviously, this treatment caught on and by the 1970s, the United States was using nearly 10 million metric tons of salt per year to de-ice roadways.

Data provided by the U.S. Geological Survey

Depending on the weather, the Ohio department of transportation will use between 300,000 and 900,000 tons of ice every winter!

Hopefully, we will not have to use much more salt this winter.