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"


  1. holy crap I worked in a steel mill for two years and never knew how coke actually worked. Now I know!! I was never anywhere near the blast furnaces though..

    one question though: how does charcoal-cooked food become carcinogenic?

  2. That rules! It must be nuts in a steel mill, I've never been in one, would love to though. If you weren't near the blast furnaces, what were you near?

    To answer your question, as far as I understand, charcoal-grilled food obtains carcinogenic chemicals when you burn the food. The carcinogens that are formed are known as polyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs), and are similar to charcoal in that they are composed almost solely of carbon. The formation of PAHs and HCAs from food is similar to the formation of charcoal from wood in that charcoal, PAHs, and HCAs are the products of incomplete combustion, where most of their hydrogen and oxygen atoms have been removed. It is also possible, though I am just speculating here, that as charcoal burns it emits PAHs that are absorbed by the food, though I believe that this would be a minor contributor.

    As far as how much burning your food in this fashion increases your risk of cancer the jury is still out on this one. What I can say is that both PAHs and HCAs have been shown to cause cancer in animal models. So, it is probably a good idea to not burn the crap out of your food. More info here:

  3. Thought this was fascinating ... the most famously carcinogenic PAH, whose presence in soot is believed to have caused the first known type of cancer (i.e., of the scrotum), benz[a]pyrene, is a pro-carcinogen: it requires oxidation by CYP450 enyzmes to give the pyrene diol/epoxide, which is basically a heat-seeking missile for DNA (its a terrific intercalating agent in addition to being a covalent modifier). But what's really interesting is the proposal that benzepyrene-diol-epoxide is especially effective targeting the gene for p53, a tumor-suppressor protein known as 'the gaurdian of the genome' ...
    also see (full text):

  4. that is to say, "especially effective" ... as a carcinogen by virtue of ... "targeting the gene ...," my bad

  5. Woah, that rules, thanks dude. Also wild that scrotum cancer was the first known type.

  6. yeah, it was called 'chimney-sweep's disease' - it was discovered in lower-class European men who swept chimneys for a living. This was before the advent of radiology, so internal tumors might have been extremely hard to detect back then; on the other hand, uncontrolled cell growth taking place in or on one's balls is probably going to get noticed before too long, especially among chimney-sweeps with wives or girlfriends (whose inadvertently investigative efforts probably save lives in the modern era).

  7. Wow, chimney-sweep's disease!! Lee, don't breathe in too much while you're taking photos of camp fires.

    To answer your question from before, I worked at LTV steel, in the most awesomely named part of the entire operation: the 84" Hot Strip Mill.

    It looked pretty much exactly like this.
    It's about a half-mile long, because there are giant slab-reheating furnaces at one end then a long series of roller "stands" that squash the hot slab down thinner and thinner as it progresses down the line. (here's a cool animation [from this wikipedia page]).
    at the end of the line, the thin steel gets wound up into a giant coil. When the slab gets to the end of the line and it's been squashed down from 9 inches to a fraction of an inch, it's traveling really fucking fast (100-200 times faster than its original speed). Sometimes it doesn't hit the coiler just right, and you get a "pile-up" which looks exactly like ribbon candy, except made out of STEEL.

  8. Regarding cancer-actually, cancer has been a known disease for just about as long as medicine has existed. The name "cancer" comes from, I believe, the writings of Hippocrates, who thought that the tumors looked something like crabs (from the Greek work karkinos). There is evidence that the Egyptians also identified and treated, at the very least, male breast cancer, though the relevant document could merely be describing to an abscess.

    The cancers growing on the intimate areas of chimney sweeps were, however, one of the first cancers to be linked to a specific cause. I believe cancer was linked with some forms of tobacco around the same time.

    1. wowzers. ancient cancer! Thanks for the info!