Coyote wrote:Just a note for fans of the BIC lighter here. At about 10F those lighters do not work as it is too cold to vaporize the butane so you have to keep them in your undershorts to keep them warm so they will work. At minus 10F I doubt you could pull it out of your shorts and start a fire before it cooled off again. Better to have more than one means to start a fire. Steve
Here's a good summary I found online a while back:
B
utane has a large vapor pressure (the enthalpy of vaporization is relatively small). This means that even at low temperatures, it will evaporate very quickly. This is especially true because the atmosphere does not normally have any butane in it - so even a small partial pressure combined with convective transport in the air will cause it to evaporate even faster. If you imagine pouring some rubbing alcohol out on a table and then putting a fan next to it, it is the same idea. Butane molecules randomly have enough energy to escape the liquid, and air currents carry them away. Since there is no butane vapor nearby to establish an equilibrium with the liquid, more butane evaporates to take its place.
The net result of this is that even if you did the experiment in a freezer and made sure everything was below −1∘C−1∘C (which includes you wearing well-insulated gloves and not breathing on it), it might still evaporate so fast that it would look as if it were boiling.
From wikipedia, here is a plot of vapor pressure vs T for butane:
The boiling point is the point where the vapor pressure line exceeds atmospheric pressure. Atmospheric pressure is usually around 760 mmHg. This is a log plot for the P axis, which means one large grid step is ten times larger than the previous one. From this graph, you can see that at −30∘C−30∘C, the vapor pressure is still ~200 mmHg. This means that roughly 26% of the air at equilibrium would be butane. Unless you have a very tiny freezer, that is a lot. This means that you might have to wear a gas mask and get a 55 gallon drum of butane before you could really do any "pouring" in the traditional sense.
At −100∘C−100∘C you are down to 1 mmHg vapor pressure. At this point I would say that even a small amount (like what is in a lighter) would stay liquid long enough that you could pour it.
Log plot of vapor pressure of butane vs temperature:
