External Temperature
Finally, with a knowledge of the Arrhenius rate-temperature relationship, it can be anticipated that burning rate will also depend on the initial temperature of the composition. Considerably more heat input is needed to provide the necessary activation energy at - 30°C than is needed when the mixture is initially at +40°C (or higher). Hence, both ignition and burning rate will be affected by variations in external temperature; the effect should be most pronounced for compositions of low exothermicity and low flame temperature. For black powder, a 15% slower rate is reported at 0°C versus 100°C, at external pressure of one atm. Some high explosives show an even greater temperature sensitivity. Nitroglycerine, for example, is 2.9 times faster at 100°C than it is at 0°C.