The Knowledge: How to Rebuild Our World From Scratch (12 page)

SUBSTANCES

The shrieks of the birds that nest out there and the distant ocean grinding against the ersatz reefs of rusted car parts and jumbled bricks and assorted rubble sound almost like holiday traffic.

M
ARGARET
A
TWOOD,
Oryx and Crake
(2003)

CHEMICALS ARE PRETTY MALIGNED
in modern society. We’re constantly being told that certain food is healthy because it includes no artificial chemicals, and I’ve even seen claims for “chemical-free” bottled water. But the fact is that pure water is itself a chemical, as is everything that makes up our bodies. Even before humanity began to settle down and the first cities were founded in Mesopotamia, our lives depended on the deliberate extraction, manipulation, and exploitation of natural chemicals. Over the centuries we’ve learned new ways to interconvert between different substances, transforming those that can be most easily acquired from our surroundings into those that we need the most, and producing the raw materials with which our civilization has been built. Our success as a species has come not just from mastering farming and animal husbandry or employing tools and mechanical systems to ease labor; it also derives from the proficiency with which we can provide substances and materials with desirable qualities.

The different classes of chemical compounds are like a carpenter’s
tool kit, each suited to perform a particular task, and we use them to transform raw materials into the products we need, wielding different tools for particular jobs. We’ll see that long, chain-like hydrocarbon compounds not only make good stores of energy, but are also water-repellent and therefore crucial for weatherproofing. We’ll take a look at different solvents for extraction or purification and investigate how alkalis and their chemical counterparts, acids, have been used throughout history for a number of critical operations. We’ll see how some chemicals are able to “reduce” others by stripping away oxygen—a fundamental capability for producing pure metals—while others, known as oxidizing agents, have the opposite action and are able to accelerate combustion, for example. Later in the book we’ll examine the chemistry of the processes that make electricity, allow us to capture light for photography, and release a burst of energy for explosives.

I’ll concentrate here on some of the most immediately useful substances and processes, a tiny subset of the whole. The fullness of chemistry is a vast network of connections, possible transformations, and conversions between different compounds, and there will be a lot of post-apocalyptic catch-up work in exploring the many features of this territory again, reconnoitering the most efficient methods, rediscovering the ideal ratios to introduce reactants together, and determining the correct chemical formulas and molecular structures.

Over time humanity has achieved ever-greater proficiency in controlling and commanding combustion—harnessing fire. Many of the basic functions of civilization rely on chemical or physical transformations driven by heat: smelting, forging, and casting metals; creating glass;
refining salt; making soap; burning lime; firing bricks, roofing tiles, and clay water pipes; bleaching textiles; baking bread; brewing beer and distilling spirits; and driving the advanced Solvay and Haber processes we’ll return to in Chapter 11. Transient bursts of fire imprisoned inside the pistons of the internal combustion engine power our cars and trucks, and every time you flick on the light switch at home, you’re still most likely using fire that has been trapped in a remote location, its energy extracted, changed in form, and then sent down wires to your electric bulb. Our modern, technological civilization is just as dependent on the basic application of fire as our ancestors cooking around the hearth in the earliest human settlements.

Today, much of this required thermal energy is provided either directly or indirectly (via electricity) from the combustion of fossil fuels: oil, coal, or natural gas.
Indeed, one of the major enabling technologies for the Industrial Revolution in the eighteenth century was the production of coke from coal and the application of this fuel to many of the processes listed above, in particular to smelting iron and producing steel. Ever since, the progress of our civilization has been powered not by sustainable means, regenerating as much as it consumes, but by plundering these deposits of fossil fuels—energy trapped in transformed vegetative matter accumulated over millions of years.

A society knocked back to basics by an apocalypse may find it difficult to provide for its thermal energy demands once the remnant stocks in gasoline stations and natural-gas storage depots are gone. Much of the easily accessible, high-quality reserves of fossil fuels have already been depleted: the cornucopia of accumulated, ready-to-go energy that gave us an easy ride the first time around is now gone. Oil is no longer found in shallow wells, and coal miners are being forced to delve deeper and deeper into the bowels of the Earth, demanding sophisticated techniques for drainage, ventilation, and
support against collapse.
*
Vast reserves of coal do remain globally: the three largest, in the USA, Russia, and China, total more than an estimated 500 million metric tons, but much of the easy-to-get coal has already been got. Some groups of post-apocalyptic survivors may be lucky enough to find themselves near surface coal deposits that can be mined open-pit, but nonetheless civilization restarting after a Fall may be forced into a green reboot.

As we saw in Chapter 1, in the first few decades after the cataclysm, forests will readily reclaim the countryside and even abandoned cities. A small recovering population of survivors will not lack firewood, especially if they maintain coppices of fast-growing trees. The basic principle of coppicing is that once cut down, ash or willow will re-sprout from their own stump and be ready for harvesting again within five to ten years, providing on average five to ten tons of wood every year from one hectare (two and a half acres) of managed forest. Wooden logs are fine for a fireplace warming the home, but for practical applications during the long recovery process you’ll need a fuel that burns much hotter than wood. And this necessitates the revival of an ancient practice: charcoal production.

The process is a simple one. Wood is burned with constrained airflow to limit oxygen availability so that it cannot combust completely, but is instead carbonized. The volatiles, such as water and other small, light molecules that turn to gas easily, are driven out of the wood, and then the complex compounds making up the wood are themselves
broken down by the heat—the wood is pyrolyzed—to leave black lumps of almost pure carbon. Not only does this
charcoal burn far hotter than its parent wood—because it’s already lost all the moisture, and only carbon fuel remains—but the loss of around half of the original weight also means that it is far more compact and transportable.

The traditional method for this anaerobic transformation of wood—the specialist craft of the collier—was to build a pyre of logs with a central open shaft, and then smother the whole mound with clay or turf. The stack is ignited through a hole in the top, and then the smoldering heap is carefully monitored and tended over several days. You can achieve similar results more easily by digging a large trench and filling it with wood, starting a hearty blaze, and then covering over the trench with scavenged sheets of corrugated iron and heaping on soil to cut off the oxygen. Leave it to smolder out and cool. Charcoal will prove indispensable as a clean-burning fuel for rebooting critical industries such as the production of pottery, bricks, glass, and metal, which we’ll come to in the next chapter.

If you do find yourself after the Fall in a region with accessible coalfields, they will again present an irresistible source of thermal energy. A single ton of coal can provide as much heat energy as a year’s firewood output of a whole acre of coppiced woodland. The problem with coal is that it doesn’t burn as hot as charcoal. It’s also pretty dirty—the fumes can taint products made using its heat, such as bread or glass, and sulfur impurities make steel brittle and troublesome to forge.
*
The trick to using coal is to first coke it, echoing the practice of
turning wood to charcoal. Coal is baked in an oven with restricted oxygen to drive out impurities and volatiles, which, like the products of timber dry distillation, have their own diverse uses and should be condensed and collected.

Combustion also provides light, and while the recovering society restores electrical grids and reinvents the light bulb, survivors will need to rely on oil lamps and candles.
*
Plant oils and animal fats are particularly well suited to serving as condensed energy sources for controllable combustion, due to their chemistry. The main feature of these compounds is their extended hydrocarbon chains: long daisy chains of carbon atoms with hydrogen atoms stuck on at the sides, adorning the flanks like stubby caterpillar legs. Energy is contained within the chemical bonds between the different atoms, and so the long hydrocarbons represent dense reservoirs waiting to be liberated. During combustion, this large compound is ripped apart, and all of the atoms unite with oxygen: the hydrogen atoms combine to form H
₂
O, water, and the carbon backbone fragments and escapes as carbon dioxide gas. The rapid disassembly of long fatty molecules during oxidation releases a torrent of energy—the warming glow of a candle flame.

An oil lamp can be as basic as a clay bowl with a pinched spout or nozzle, or even just a large shell. A wick, made of plant fiber such as flax or simply rush, draws the liquid fuel up from the reservoir to be evaporated by the warmth of the flame and then combusted. Kerosene has been a common liquid fuel for glass lamps since the 1850s (and today also powers passenger jet planes over the clouds), but it is derived
from the fractional distillation of crude oil and would be difficult to produce after the collapse of modern technological civilization. Any unctuous liquid suffices, though: rapeseed (canola) or olive oil, or even ghee from clarified butter.

A candle can dispense with the container altogether because the fuel itself remains hard until melted in a small pool in the vicinity of the flame—thus a candle is no more than a cylinder of solid fuel with the wick running down the middle. As it burns down, more wick is exposed, producing a larger and smokier flame, unless you periodically snip the wick. The fuss-saving innovation, which didn’t occur to anyone until 1825, is to braid the fibers of the wick as a flattened strip, so that it naturally curls over and the excess is consumed by the flame.

Modern candles are composed of wax derived from crude oil, and the availability of beeswax will always be limited, but you can make a perfectly functional candle from rendered animal fat. Boil meat trimmings in salty water, and scoop the hardening layer of floating fat off the surface. Pig lard produces a smelly, smoky candle, but beef tallow or sheep fat are passable. Pour molten tallow into a mold, or even just dip a row of dangling wicks into hot tallow to coat them; allow them to cool and set in the air. Then repeat, building up layer after layer until you have substantial candles.

The first substance that a recovering post-apocalyptic society will need to begin mining and processing for itself, because of its multitude of functions that are absolutely critical to the fundamental operations of any civilization, is calcium carbonate. This simple compound, and the derivatives easily produced from it, can be used to revive agricultural productivity, maintain hygiene and purify drinking
water, smelt metals, and make glass. It also offers a crucial construction material for rebuilding and provides key reagents for rebooting the chemical industry.

Coral and seashells are both very pure sources of calcium carbonate, as is chalk. In fact, chalk is also a biological rock: the white cliffs of Dover are essentially a 100-meter-thick slab of compacted seashells from an ancient seafloor. But the most widespread source of calcium carbonate is limestone. Luckily, limestone is relatively soft and can be broken out of a quarry face without too much trouble, using hammers, chisels, and pickaxes. Alternatively, the scavenged steel axle from a motor vehicle can be forged into a pointed end and used as a drill to repeatedly drop or pound into the rock face to create rows of holes. Ram these with wooden plugs and then keep them wet so that they swell and eventually fissure the rock. But pretty soon you’ll want to reinvent explosives and use blasting charges to replace this backbreaking labor.

Calcium carbonate itself is routinely used as “agricultural lime” to condition fields and maximize their crop productivity. It is well worth sprinkling crushed chalk or limestone on acidic soil to push the pH back toward neutral. Acidic soil decreases the availability of the crucial plant nutrients we discussed in Chapter 3, particularly phosphorus, and begins starving your crops. Liming fields helps enhance the effectiveness of any muck or chemical fertilizers you spread.

It is the chemical transformations that limestone undergoes when you heat it, however, that are particularly useful for a great range of civilization’s needs. If calcium carbonate is roasted in a sufficiently hot oven—a kiln burning at least at 900°C—the mineral decomposes to calcium oxide, liberating carbon dioxide gas. Calcium oxide is commonly known as burned lime, or quicklime. Quicklime is an extremely caustic substance, and is used in mass graves—which may well be necessary after the apocalypse—to help prevent the spread of diseases and to control odor. Another versatile substance is created by carefully
reacting this burned lime with water. The name quicklime comes from the Old English, meaning “animated” or “lively,” as burned lime can react so vigorously with water, releasing boiling heat, that it seems to be alive. Chemically speaking, the extremely caustic calcium oxide is tearing the molecules of water in half to make calcium hydroxide, also called hydrated lime or slaked lime.

Hydrated lime is strongly alkaline and caustic, and has plenty of uses. If you want a clean white coating for keeping buildings cool in hot climes, mix slaked lime with chalk to make a whitewash. Slaked lime can also be used to process wastewater, helping bind tiny suspended particles together into sediment, leaving clear water, ready for further treatment. It’s also a critical ingredient for construction, as we’ll see in the next chapter. It’s fair to say that without slaked lime, we simply wouldn’t have towns and cities as we recognize them. But first, how do you actually transform rock into quicklime?

Modern lime works use rotating steel drums with oil-fired heating jets to bake quicklime, but in the post-apocalyptic world you’ll be limited to more rudimentary methods. If you’re really pulling yourself up by your bootstraps, you can roast limestone in the center of a large wood fire in a pit, crush and slake the small batches of lime produced, and use them to make a mortar suitable for building a more effective brick-lined kiln for producing lime more efficiently.

The best low-tech option for burning lime is the mixed-feed shaft kiln: essentially a tall chimney stuffed with alternating layers of fuel and limestone to be calcined. These are often built into the side of a steep hill for both structural support and added insulation. As the charge of limestone settles down through the shaft, it is first preheated and dried by the rising draft of hot air, then calcined in the combustion zone before it cools at the bottom, and the crumbling quicklime can be raked out through access ports. As the fuel burns down to ash and the quicklime spills out the bottom, you can pile in more layers of fuel and limestone at the top to keep the kiln going indefinitely.

A shallow pool of water is needed for slaking the quicklime, and you could use a salvaged bathtub. The trick is to keep adding quicklime and water so that the mixture hovers just below boiling, using the heat released to ensure that the chemical reaction proceeds quickly. The fine particles produced will turn the water milky before gradually settling to the bottom and agglutinating as the mass absorbs more and more water. If you drain off the limewater, you’ll be left with a viscous sludge of slaked-lime putty. We’ll see in Chapter 11 how limewater is used to produce gunpowder, but let’s look here at one particularly useful application of slaked lime: to create a chemical weapon against marauding hordes of microorganisms.