... Then they got really smart. Certain chemical processes can "bend" (not a precise scientific term here folks, but close enough) the butane molecule into what's called an isomer. The isomer has the same chemical formula (C4H10), but it's different geometry gives it different properties, one property is that the point at which it vaporizes goes from 31F to 11F.
Very interesting, thanks! I assume this is what's referred to as isobutane?
Exactly. The isomer form of butane is isobutane, and any time you're out in weather that's going to be below 50F, then it's worth your while to only get brands with isobutane. "Plain" butane does not work well for canister gas stoves in cold weather.
Also, if propane vaporizes down to -44F, why not fill the canister 100% with propane, and forget about the butane completely?
Ah! The classic question. Well, think about a pot on the stove that's gently boiling. Then you open up the burner on full, the boil goes wild, and the lid practically jumps off the pot. What's happening here? The higher above the boiling point in terms of temperature, the more vigourous the boil, and the greater the vapor pressure. Propane vaporizes at -44F. If one is at, say, +100F, one is some 144 Fahrenheit degrees above the boiling point of propane. The vapor pressure is so high that a thin walled steel canister (such as those used for backpacking) cannot safely contain the pressure. Therefore, in the US, you won't find more than 30% propane/70% butane (or 20% propane/80% isobutane) mixes. They just won't meet safety standards. That's the simplest answer I can give. Physicists and chemists among you will no doubt point out that smaller, lightweight canisters that would contain 100% propane are possible, but such canisters would not be as affordable as the current cheap steel canisters commonly used today. However, if anyone wants to provide me with a titanium canister for me to experiment with, I am all ears.
HJ
