Basic Chemistry
While I am not a chemist, I do teach it on a daily basis...
A "pure" substance (the diesel fuel or the additive) has a given freezing point. Add two substances together, and the freezing point drops (pure water freezes at 0 degrees Celcius, add salt in a 4:1 ratio, and the freezing point drops to -11 degrees Celcius). Same is true for boiling points, except that they are raised (adding salt to water for making pasta - the pasta cooks quicker because the boiling point is higher).
- frank