Tuesday, January 4, 2011

Why Fire is Cool - entry #2 - How Charcoal Changed the World

Entry #2 in my "why fire is cool" list starts with a brief introduction to charcoal and ends with humanity being changed forever.  It was around the time that I was waiting for the kebabs in the picture below to come off the grill that I learned what charcoal is, and that excited just about as many neurons in my brain as did eating the savory kebabs.
Charcoal is carbon!  Charcoal comes from wood (duh), but what is really cool is how that is done.  As we saw in the last post about the nature of fire, if you heat wood until it burns, all of the molecules that comprise wood will turn into carbon dioxide, water, and energy:
Wood + Oxygen  CO2 + H2O + energy
In order to make charcoal, you burn wood but you limit the amount of air (oxygen) it is exposed to, so instead of complete combustion, it looks more like this:
Wood + Oxygen  CO2 + H2O + energy + Charcoal
By doing this, the wood is only partially burnt, and most of the hydrogen and oxygen atoms are removed as carbon dioxide and water, leaving behind a big chunk of carbon.  Charcoal is carbon!
Aside (skip if boredom is imminent): Charcoal is useful for barbecuing in part because it burns slowly.  It burns this way because the molecular structure of the wood has been re-organized and the volatile molecules that cause wood to burn quickly (such as resin, resin acids, retene, etc) have been removed.  Fore more, go here and here.
So, fire is cool because it not only gave us humans energy, but it also gave us carbon in the form of charcoal.  As I will describe below, carbon has had impacts on the course of human civilization much more profound that the facilitation of awesome cookouts.

Carbon has changed all of our lives by allowing us to transform minerals found in the earth's crust into the extraordinarily useful metal elements copper and iron.  As I have covered before in this blog, many elements are found in the earth's crust chemically bonded with oxygen.  This is no exception for copper and iron, though copper can sometimes be found in its pure, elemental form.  Copper is found in oxidized form in the beautiful minerals azurite and malachite, and iron oxides can be found in the minerals hematite and magnetite.  So before humans could use copper and iron to make axes, swords, space ships, and iPods, we had to figure out a way to get rid of those pesky oxygen atoms.  Here is where our good friend carbon comes in.  Humans figured out how to take the copper oxides and iron oxides and heat the crap out of them in the presence of carbon in blast furnaces.  In this process, known as smelting, the oxygen atoms from the metal atoms hop over onto the carbon atoms and fly out of the top of the furnace as carbon dioxide, leaving the liquid metal to flow out of the bottom of the furnace to be cast into blocks (aka ingots) of copper or iron.
C + 2 CuO  CO2 + 2 Cu + energy
Copper ingots look something like this at first:

But after around 5,000 years they look something like this (it is green because oxygen atoms from our atmosphere have slowly re-attached themselves to the copper):

So fire not only gave humans a readily available source of energy, it also gave us carbon, which we used to isolate the metals copper and iron.  In this way the discovery of fire brought us through the stone age and into the bronze age (bronze = copper + tin) and iron age, forever changing the course of human civilization.

Related Posts:
FirePost #1: "What are Flames Made Of?"
FirePost #3: "Ash Ash Baby"
FirePost #4: "Ancient Energy Unleasher"