It’s winter- almost. But, even so, we’ve had freezing rain and snow all over the US.
Which means I have the chance to teach you a little bit of chemistry.
Sure, you know that ice forms at 32 F (O C). But, that’s only true for pure water and standard atmospheric pressure. When stuff is dissolved in the water, then the temperature at which water freezes is lower.
When you add standard salt (sodium chloride) into the mix, then for each molecule of sodium chloride added, you get two ions- and freezing is a colligative property; that means the number of particles dissolved affect the amount the freezing point is depressed. If you used sugar (sucrose), you’d only get one particle.
But, if the water contained all the salt it could hold, you could only lower the temperature of freezing to 0 F (-18 C). Which means this sort of solution won’t work in the US Midwest or Canada, where the temperatures drop below this level. More importantly, no one wants to add that much salt (35% by weight) to the roads- it’s expensive and corrosive to everything it touches.
So, we use different concoctions. Some areas use mixtures of calcium chloride (which provides 3 and not 2 ions upon dissolution- more colligative effects). But, some places have begun to use beet juice mixtures. The stuff that comes from sugar beet molasses (it’s a saturated solution, with about 55% solids content.)
The mixture that seems most prevalent to be applied to our roads is comprised of 23% salt, 15% beet juice, with the rest being water (62%). The mixture is not red, but amber- and it’s sticky. Oh, it’s easily spread by the ‘snow trucks’, too. Another factor- this sticky mess stays on the road. Dry salt tends to wash off the roads.
There’s another advantage to using this mixture. The salt sprays really don’t do any good once the temperature drops below 20 F (- 7 C); the beet juice concoction holds off the ice when the temperature dips below – 20 F (- 29 C)– maybe even to – 30 F (-35 C). And, those temperatures don’t really obtain in the States.
(By the way, this concoction came into use from ‘observation’- one of the scientific principles. It seems that sugar beet processing plants in certain less-than-advanced nations are not very secure about their effluent discharges. And, it was noted that ponds near the facilities would not freeze up- which meant that the beet runoff was involved in this phenomenon. At least something positive came forward from this environmental failure.)
