It's cold out there! What to use?
Most deicer bags and literature show a number — the lowest melting temperature at which the product works. There are two tricks involving this number.
First, some products use an ice melting temperature created in a laboratory under perfectly controlled conditions and concentrations of chemical. This is known as the eutectic temperature. You will not be able to reproduce those conditions. The only temperature of importance is the practical temperature. Practical is defined as being effective within 15 minutes of application.
Blending temperature tricks
The second temperature trick applies only to blended products — those with more than one ingredient. The vast majority of blended ice melters contain over 50% sodium chloride. Most contain at least 90% salt. A hypothetical deicer containing 90% salt and 10% calcium chloride will illustrate the trick. That product can legally be labeled as being effective to -59°F — the eutectic temperature for calcium chloride. But, in fact, not only is 90% of the product, salt, ineffective below +20°F, the calcium chloride is only effective to -25°F.