In fact, salt does not actually melt ice! What actually happens is that as salt is sprinkled on snow, the freezing point of the water (the ice) is lowered, which is why the snow or ice melts away.
This explains why, all else being equal, the freezing point of ice is 0 degrees Celsius, but the freezing point of sea water (which is saline, due to the presence of salt in it) is lower (-2.2 degrees Celsius).
So as salt is gritted onto our roads, the freezing point of the ice (in the snow) is lowered, which is why the snow or ice melts away.
Gritting: The Battle of Salt vs. Ice
As temperatures drop, you do need more salt for every pound of ice that you want to melt.
At a temperature of -1oC, one pound of salt will melt 46 lbs of ice.
And, at the 'Eutectic' point salt will not melt ice at all (-21oC).
What does Ice Cream Have to do with Salt?
Interesting fact: in order to make ice cream you need to add salt. Why?
Ice melts and and grows warm well before ice cream making is complete.
So it's worth taking a moment this summer's day to be grateful for salt, both for keeping the roads and paths safe in winter, and keeping you cool in summer.
Types of Salt
There are two main types of salt in use for melting ice, rock salt and marine salt.
Rock salt tends to be brown, whereas marine salt is purest white.
Rock salt is the commoner of the two, and widely used by councils in the UK.
Marine salt tends to be used by professional operators, as it has a higher percentage of NaCl, and also it does not leave any residue that needs to be cleared away.
How Much Salt Is Used In The UK?
More than two million tonnes of salt are spread onto the UK roads each year, costing more than £150 million per year.
The majority of this is spread onto motorways, trunk roads and main roads, with less than a third allocated to small country roads.
Research has shown that for every £1 expended on winter road maintenance, about £8 is saved in the economy as a whole.
And this does not even take into account the potential for human tragedy.
The cost of an accident or fatality on the roads is huge when items such as health care and legal costs are included.