As the story goes, the tin buttons on the coats of Napoleon’s troops literally crumbled to a powder after being exposed to the bone-chilling cold of a Russian winter. The culprit? A metastable material, pure tin undergoes a structural transformation at low temperatures (below 0C), essentially decomposing into dust.
This transformation is called tin pest, which can be avoided by combining tin with other elements, like, you know, lead.
Given the much debated issue over the reliability of new lead-free solders dictated by RoHS regulations that went into effect last year, the button story is making its rounds again in engineering circles, including here in this blog. And that of course got me wondering whether there is any shred of truth to the tale.
“It’s a story that virtually every chemistry student has heard, but we don’t really know if Napoleon’s army actually had buttons made of tin,” says Penny LeCouteur. She’s co-author of the book “Napoleon’s Buttons” How 17 Molecules Changed History,” a highly entertaining look at chemical compounds and their impact on the course of history.
It’s a ripping good read:
There are many stories that engineers will remember or can relate to, like the O-ring failure on the NASA space shuttle with just enough science to be credible without feeling the need to run for your CRC Handbook of Chemistry and Physics.
Though the section on Napoleon’s wardrobe is a mere couple of pages, LeCouteur, a former chemistry professor and now administrator at Capilano College, says that while she was researching the book she was struck by photos of old tin vessels that are now in museums. “What amazed me was that they no longer had that sharp outline to their geometries, which made sense because these objects were exposed to the frigid winters in northern Europe. Victims of tin pest, the outer layers simply turned to powder and sloughed off. “ Theoretically, Lecouteur says that the same thing could have happened to Napoeleon’s buttons. But she says that there is simply not enough evidence to conclude that it did.
“There were eyewitness accounts and you do see paintings that were made of Napoleon and his troops at that time holding old carpets and blankets around themselves to keep warm, so we do know about the kind of cold they had to endure. But buttons made out of pure tin would have been quite expensive compared to wood or bone. And chemically, tin pest is a very slow process.”
In fact, LeCouteur says that a colleague stuck a pot of tin in his fridge as an experiment. “After several months, he couldn’t detect any difference in the sample. So it’s likely Napoleon’s troops would have had to endure some hellishly long winters before their buttons distintegrated.”