The hydrolysis reaction that transforms animal fats into soap is also used for making glue. It’s created by boiling skin, sinew, horns, or hooves: anything that contains tough connective tissue made of collagen, which disintegrates to gelatin. This dissolves in water, so can be formed into a gloopy, tacky paste that then dries hard and firm. The necessary hydrolytic breakdown of collagen is much faster under strongly alkaline or acidic conditions—another application for lye, or for acids (which we’ll come to in a bit).
WOOD PYROLYSIS
Wood can offer so much more than just carbon fuel and alkali from its ashes. In fact, wood was once the major source of organic compounds—providing chemical feedstocks and precursor substances for a vast array of different processes and activities—and was superseded only in the late nineteenth century by coal tar and the subsequent development of petrochemicals from crude oil. In a post-apocalyptic world, therefore, where you may well find yourself without accessible coal or a continuing supply of oil, these older techniques will support the rebooting of a chemical industry.
A SIMPLE SETUP FOR THE PYROLYSIS OF WOOD AND COLLECTION OF THE VAPORS RELEASED (TOP), AND SCHEMATIC OF THE DIVERSE CRUCIAL SUBSTANCES THAT CAN BE DERIVED IN THIS WAY (BOTTOM).
The whole point of charcoal making is to drive out the volatiles from wood to leave a hot-burning fuel of almost pure carbon, but these volatile “waste” products are in fact very useful. And with a little refinement of charcoal production, these escaping vapors can also be captured. By the second half of the seventeenth century, chemists had noticed that burning wood in a closed container released flammable gas and also vapors that could be condensed back into a watery fluid. These products came to be known as pyroligneous (a Greek-Latin hybrid word for fire and wood) and are a complex mixture of many different compounds. An ideal stepping-stone for a recovering society to leapfrog to would be to bake wood in a sealed metal compartment, with a side pipe drawing off the released fumes and coiling through a bucket of cold water to cool and condense the vapors. The released gases do not condense, and so can be used to fuel the burners beneath the wood-baking compartment. We’ll see in Chapter 9 how these pyroligneous gases can even be used to fuel a vehicle.
The collected condensate readily separates into a watery solution and a thick tarry residue, both of which are complex mixtures that can be teased apart by distillation, as described earlier. The watery part, originally termed pyroligneous acid, is mainly composed of acetic acid, acetone, and methanol.
Acetic acid, as we’ve seen, can be used for pickling food: vinegar is essentially a dilute solution of acetic acid. It reacts with alkaline metal compounds to produce various useful salts. For example, it can react with soda ash or caustic soda to produce sodium acetate, which is useful as a mordant to fix dyes to cloth. Copper acetate works as a fungicide and has been used since antiquity as a blue-green pigment for paints.
Acetone is a good solvent and is used as the base for paints—it is the distinctive scent of nail polish—and as a degreaser. It is also important in plastics production and is used in the making of cordite, the explosive propellant used for bullets and shells during the First World War. In fact, there was a point when Britain feared losing the war due to an acute shortage of acetone. The huge demand for cordite far exceeded what could be produced by the dry distillation of wood, even with imports of the solvent from timber-rich countries like the United States. Production was maintained by the invention of a new technique, using a particular bacterium to secrete acetone during fermentation, and huge amounts of horse chestnuts collected by schoolchildren as the feed.
Methanol, originally known as wood spirits, is produced in large amounts by the dry distillation of wood: every ton of timber yields about ten liters. Methanol is the simplest alcohol molecule: it contains only one carbon atom, whereas ethanol, or drinking alcohol, is built around a backbone of two. Methanol can be used as a fuel and a solvent; it functions as antifreeze and is also crucial in the synthesis of biodiesel, which we will come to in Chapter 9.
The crude tar sweated out of the roasted wood can also be separated by distillation into its major constituents: thin, fluid turpentine (floats on water); thick, dense creosote (sinks in water); and dark, viscous pitch. Turpentine is an important solvent, used historically for pigments, and we’ll come back to this in Chapter 10. Creosote is a fantastic preservative, and when painted on or soaked into wood protects it against the elements and rot. It also acts as an antiseptic, inhibiting microbial growth and preserving meats: it is responsible for the distinctive flavor of smoked meats and fish. Pitch is the gloopiest of the extracts, a viscous mixture of long-chain molecules, and its flammability is ideal for soaking into wooden rods to make torches. This tarry substance is also water-repellent and useful for sealing buckets or barrels; it has been used for millennia to caulk the seams between the wooden slats of a boat’s hull.
The timber of any tree will provide differing quantities of these crucial chemicals by dry distillation, but resinous hardwoods, including conifers such as pines, spruces, and firs, yield more pitch. Birch bark is a particularly good source of pitch that has been used since the Stone Age to stick fletching feathers to arrows. Indeed, if it is only the pitch you’re after, you can collect it as it oozes out of resinous wood baked in a kiln, or even just in a tin box tossed on a fire.
Distillation is such a universally useful technique for separating a blend of fluids, exploiting the principle that different liquids boil at specific temperatures, that a recovering society would do well to master it as early as possible. Distillation fractionates, or separates, the various products of heat-decomposed wood and extracts concentrated alcohol from a fermented slop, as we’ve already seen; it also teases apart crude oil into a diverse selection of different constituents, from thick viscous asphalt to light volatile components like gasoline. And once a certain level of industrial capability is achieved, even air itself can be distilled. The gas mixture is chilled to around -200°C by using a repeated expansion and cooling process and is held in a vacuum-insulated capsule, like a giant thermos flask for taking coffee on a hike. The liquid air is then allowed to warm, and as each separate gas boils off it is collected, the pure oxygen used, for example, for hospital breathing masks.
ACIDS
So far we’ve focused mainly on alkalis, as strong varieties are relatively easy to make. Acids, their chemical counterparts, are just as common in nature, but particularly potent kinds are harder to come across than lyes and have been significantly exploited only more recently in history. We have seen how a variety of plant products can be fermented to produce alcohol, and that this ethanol can in turn be oxidized by exposure to air to produce vinegar. Acetic acid was the earliest acid available to humanity, and for the great majority of history it was also our only option. Civilization has been able to choose from a selection of alkalis—potash, soda ash, slaked lime, ammonia—but for millennia our chemical prowess was limited by wide availability of but a single weak acid.
The next acid to be exploited by humanity was sulfuric acid. This was initially baked out of a rare glass-like mineral called vitriol, and later mass-produced by burning pure yellow sulfur with saltpeter (potassium nitrate) in steam-filled, lead-lined boxes. Today we make sulfuric acid as an offshoot of scrubbing oil and natural gas to remove the sulfur contaminants. So in a post-apocalyptic world you might be caught in the middle: unable to create this crucial, potent acid using traditional methods, as elemental sulfur has long since been removed from surface volcanic deposits, and incapable of pulling off more advanced techniques without the specific catalyst needed.
The trick is to employ a chemical pathway that was never used industrially in our development. Sulfur dioxide gas can be baked out of common pyrite rocks (iron pyrite is notorious as fool’s gold, and pyrites also form common ores of lead and tin) and reacted with chlorine gas, which you get from the electrolysis of brine, using activated carbon (a highly porous form
of charcoal) as a catalyst. The resulting product is a liquid called sulfuryl chloride that can be concentrated by distillation. This compound decomposes in water to form sulfuric acid and hydrogen chloride gas, which should itself be collected and dissolved in more water for hydrochloric acid. Luckily, there is also a simple chemical test for whether a rock is a pyrite mineral (a metal sulfide compound): dribble a little dilute acid on the rock, and if it fizzes and gives off the stench of rotting eggs, you’ve got what you’re after (but hydrogen sulfide gas is poisonous, so don’t sniff too much!).
Today, more sulfuric acid is manufactured than any other compound—it is the linchpin of the modern chemical industry, and will also be crucial in accelerating a reboot. Sulfuric acid is so important because it’s good at performing several different chemical functions. Not only is it potently acidic, it is also strongly dehydrating and a powerful oxidizing agent. Most of the acid synthesized today is used to produce artificial fertilizers: it dissolves phosphate rocks (or bones) to liberate the crucial plant nutrient phosphorus. But its uses are virtually limitless: preparing iron gall ink, bleaching cotton and linen, making detergents, cleaning and preparing the surface of iron and steel for further fabrication, creating lubricants and synthetic fibers, and serving as battery acid.
Once you’ve reacquired sulfuric acid, it serves as a gateway to the production of other acids. Hydrochloric acid is produced by reacting sulfuric acid with common table salt (sodium chloride), and nitric acid comes out of the reaction with saltpeter. Nitric acid is particularly useful because it is also a very potent oxidizing agent: it can oxidize things that sulfuric acid can’t. This makes nitric acid invaluable for creating explosives as well as for preparing silver compounds for photography—two key processes that we will return to later.
CHAPTER 6
MATERIALS
There was on this continent a more advanced civilization than we have now—that can’t be denied. You can look at the rubble and the rotted metal and know it. You can dig under a strip of blown sand and find their broken roadways. But where is there evidence of the kind of machines your historians tell us they had in those days? Where are the remains of self-moving carts, or flying machines?
WALTER M. MILLER JR, A Canticle for Leibowitz (1960)
AS IS OBVIOUS FROM THE LAST CHAPTER, it is difficult to overstate the sheer usefulness of wood. Its chemical potential aside, timber is one of the most ancient building materials, providing beams, planks, and poles for construction. The particular qualities of different trees are suited to different applications, and there is an enormous amount of accumulated knowledge that would need to be rediscovered by a fledgling civilization after the apocalypse. For example, elm wood’s tough, interlocked fibers resist splitting, and it’s therefore ideal for cart wheels. Hickory is particularly hard and thus suitable for the gear teeth of the power mechanisms in windmills and water mills. Pine and fir trees grow exceptionally straight and tall, and so make perfect ships’ masts.
Beyond these mechanical properties, wood fires will keep the cold at bay once central heating systems have died, and will cook your food to inactivate microbial contamination and help release nutrients. The last chapter showed how to collect the vapors anaerobically baked out of timber to yield a selection of crucial substances: feedstock for rebooting a chemical industry. We’ve also seen how the resultant charcoal is ideal for filtering drinking water once the taps have run dry and bottled water has disappeared from supermarket shelves. Wood also provides hot-burning fuel for kilns firing pottery and bricks, for making glass, and for smelting iron and steel.
Immediately after the apocalypse you’ll be able to simply occupy existing buildings, repairing and patching them up as best you can. But all uninhabited and untended buildings will inexorably decay and collapse over the first decades, and as the surviving population grows and needs new homes, you’ll probably find it much easier to construct anew than try to restore the rotting shells of the old civilization. And to do that, you’ll need to learn the basics. Brick, glass, concrete, and steel are the literal building blocks of our civilization. But they all come from the humblest of beginnings: mucky earth, soft limestone, sand, and rocky ore that we dig from the ground and transmute with fire into the most useful materials of history. We can see this process most easily with clay, which is shaped and formed while soft and malleable before being heated in a kiln into a hard ceramic. We deliberately change the properties of a substance to suit our application.
CLAY
It is easy to overlook clay in our modern lives—it’s perhaps something you associate only with art lessons at school. But the truth is that pottery played an utterly pivotal role in creating the prerequisite conditions for the founding of civilization itself. Lidded receptacles fashioned out of clay enable food to be stored; protect it from pests and vermin; allow for cooking, preservation, and fermentation; and make foodstuffs far more portable for both traveling and trade. Clay formed into blocks and then fired to make bricks also provides a fabulous building material: the fabric of towns, mills, and factories.
Clay beds are exceedingly widespread, and lie beneath the topsoil in many areas of the world. Clay is made up of very fine particles of aluminosilicate mineral—sheets of aluminum and silicon, each bound to oxygen—weathered out of rocks and often transported over great distances by rivers or glaciers before being deposited. Various kinds of clay can therefore be simply dug out of pits in the ground and formed by hand. The most rudimentary receptacle can be formed from a moist ball of clay by pinching into the middle with your thumbs and smoothing into a round bowl. But for far more control over the process, you’ll want to redevelop the potter’s wheel. The earliest kind was simply a freely rotating disk, so that the workman could turn the piece around as he worked. The “modern” potter’s wheel, at least 500 years old and perhaps much more ancient, uses a spinning flywheel, such as a heavy rounded stone, to store rotational momentum and keep the piece turning smoothly as the potter works on it. The wheel is spun up every now and then with a push or kick, or, if you can scavenge one after the Fall, an electric motor.
Dried clay is relatively durable, but ideally you want to fire it to create ceramic. At temperatures between about 300° and 800°C, the water is driven irreversibly out of the clay structure, and the mineral plates lock together but remain porous. Heat it even further, to above 900°C, and the clay particles themselves begin to fuse together, and minor impurities in the clay melt. These vitrifying compounds soak throughout the piece, and when cool they solidify into a glassy matrix, firmly fusing together the clay crystals and filling any gaps to form a hard and watertight material. Deliberately dunking the piece in such substances before the high-temperature firing to seal the surfaces is the art of glazing. You can even just toss some salt into the kiln: the withering heat dissociates the compound, and sodium vapor mingles with the silicon in the clay to form a glassy coating (although noxious chlorine gas is released in the process). This method was historically employed as an easy way to waterproof clay pipes to be used for water distribution or sewer systems.
Fired clay is not just hard and watertight, it is also exceedingly heat-resistant. The aluminosilicate has an extremely high melting point, and since the constituents are already bonded to oxygen, the mineral does not combust when hot. Firebricks are therefore the perfect material to line kilns and furnaces. In order to contain fire, and therefore be able to technologically employ it, you need a substance that can insulate the heat inside but is also able to resist the temperature itself. This is a great example of a recovering civilization pulling itself up by its own bootstraps: baking clay in a large fire into a refractory material enables survivors to build further kilns to fire yet more bricks. The story of civilization itself has been an epic of the containment and harnessing of fire with ever greater finesse to attain ever higher temperatures: from the cooking campfire to the pottery kiln, the Bronze Age smelter, the Iron Age furnace, and the blast furnace
of the Industrial Revolution—and it is refractory bricks that have enabled all of this.
Fired clay is also used very commonly as a structural material. In drier climates you can get away with building a rudimentary wall out of sun-dried mud—adobe—but this is at risk of being washed away in a heavy downpour. A far more resilient brick is made by taking a few generous handfuls of clay, squashing it into a cuboidal shape in a mold, and then baking it in a kiln to drive the chemical transformations for a hard, durable ceramic. But you’re going to need more than handfuls of clay to rebuild civilization. For a sturdy wall, the rows of bricks will need to be glued together—and for that, we come back to lime.
LIME MORTARS
We saw in Chapter 5 that the first material you’re likely to need to start mining again, once the remnant commodities left behind by our current society have been depleted, is limestone. We know limestone plays a central role in synthesizing many of the crucial substances needed by a civilization. Now we’ll take a look at how the same wonder material will form the basis of rebuilding in the aftermath. Limestone blocks are useful as a construction material—as is its metamorphic product marble, formed from limestone pressure-cooked deep underground—but it is what this rock can be turned into that is so useful for rebuilding.
Slaked lime is able to transform from a spreadable paste back into a material set hard as stone. Mixed with a little sand and water, slaked lime forms mortar, which has been used to firmly stick bricks together into sturdy load-bearing walls for thousands of years. Mix it with less sand, and perhaps stir in some fibrous material like horsehair, and you have a plaster for spreading as a smooth finish on walls.
The Knowledge: How to Rebuild Our World From Scratch Page 12