h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

At what temperature does an average bar of soap melt?

I just got to wonder about it, because of the latest posting ("When A Solid Is A Liquid") on:

http://www.phdcomics.com/blog.php?postarchive=1&next=1188501711

(From personal experience, chocolate seems to melt at an earlier temperature.)

Your basic soap isn't a pure compound but tends to be a mixture of the sodium salts of the fatty acids like oleic, stearic and palmitic acids.

Sodium stearate has a melting point of 245-255 degrees C.
This would be pretty typical.

or rather melting range.

Mixtures of compounds depress the melting point of their pure components so I would imagine a bar of soap would have a wider melting range at a slightly lower temperature - say around the 230 degree mark.

Traveller in Time about
"Black (pure) chocolate melts at 38 C white just below 30 C. "

Chocolate actually has a fascinating set of phase changes. We used to use chocolate rolling mills to model the phase changes in carbon steel.

B

Traveller in Time curious
"Do the chocolate rolls require inspection ? "

Soap is used to gauge the melting point of aluminium. It is smeared on the test piece and then heated. When the soap turns black, the aluminium is workable. Just before the aluminium becomes molten, you can see the blackened soap begin to run. The melting point of aluminium is about 660 degrees Celsius, so I would deduce soap to have a melting point a few degrees below this.