The Knowledge: How to Rebuild Our World From Scratch (13 page)

Soap can be made easily from basic stuff in the natural world around you and will be an essential substance in the aftermath for averting a resurgence of preventable diseases. Health education studies in the developing world have found that nearly half of all gastrointestinal and respiratory infections can be avoided simply by regularly washing your hands.

Oils and fats are the raw material of all soaps. So, somewhat ironically, if you carelessly splash bacon fat onto your shirt cooking breakfast, the very substance you use to clean it out again can itself be derived from lard. Soap lifts greasy stains from your clothes and washes the bacteria-laden oil off your skin because it is able to mingle comfortably with both fatty compounds and water, which do not themselves mix. It takes a special kind of molecule to display this social-butterfly behavior: one with a long hydrocarbon tail that mixes with fats and oils and a charged head that dissolves well in water. An oil or fat molecule is itself composed of three “fatty acid” hydrocarbon chains all stuck onto a linker block. The key step in making soap, known as the
saponification reaction, is to snap the chemical bonds attaching the three fatty acids. A whole category of chemicals known as alkalis are able to do this, “hydrolyzing” the connector bond. Alkalis are the opposites of acids, and when the two meet they neutralize each other to produce water and a salt. Common table salt, sodium chloride, for example, is formed by the neutralization of alkaline sodium hydroxide with hydrochloric acid.

So to make soap, you need to produce a fatty acid salt by hydrolyzing lard with an alkali. While it’s true that oil and water don’t mix, this fatty acid salt can embed its long hydrocarbon tail into the oil and leave its head poking out to dissolve in the surrounding water. Coated with a fur of these long molecules, a small droplet of oil is stabilized in the midst of the water that rejects it, and so grease can be lifted off skin or fabric and be washed away. The bottle of “invigorating, reviving, hydrating, deep clean sea splash” men’s shower gel in my bathroom lists nearly thirty ingredients. But alongside all the foaming agents, stabilizers, preservatives, gelling and thickening agents, perfumes, and colorants, the active ingredient is still a soap-like mild surfactant based on coconut, olive, palm, or castor oil.

The pressing question, therefore, is where to get alkali in a post-apocalyptic world without reagent suppliers. The good news is that survivors can revert to ancient chemical extraction techniques and the most unlikely-seeming source: ash.

The dry residue left behind after a wood fire is mostly composed of incombustible mineral compounds, which give ash its white color. The first step to restarting a rudimentary chemical industry is alluringly simple: toss these ashes into a pot of water. The black, unburned charcoal dust will float on the surface, and many of the wood’s minerals, insoluble, will settle as a sediment on the bottom of the pot. But it is the minerals that do dissolve in the water that you want to extract.

Skim off and discard the floating charcoal dust, and pour out the water solution into another vessel, being careful to leave behind the
undissolved sediment. Drive off the water in the new vessel by boiling it dry, or if you’re in a hot climate, pour the solution into wide shallow pans and allow it to dry in the warmth of the sun. What you’ll see left behind is a white crystalline residue that looks almost like salt or sugar, called potash. (In fact, the modern chemical name for the predominant metal element in potash derives its name from this vernacular: potassium.) It’s crucial that you attempt to extract potash only from the residue of a wood fire that burned out naturally and wasn’t doused with water or left out in the rain. Otherwise, the soluble minerals we are interested in will already have been washed away.

The white crystals left behind are actually a mixture of compounds, but the main one from wood ash is potassium carbonate. If you burn a heap of dried seaweed instead and perform the same extraction process, you can collect soda ash, or sodium carbonate. Along the western shoreline of Scotland and Ireland the gathering and burning of seaweed was a major local industry for centuries. Seaweed also yields iodine, a deep-purplish element that you’ll find very useful as a wound disinfectant as well as in the chemistry of photography, which we’ll come back to.

If you follow the process described above, you can collect about a gram of potassium carbonate or sodium carbonate from every kilogram of wood or seaweed burned—that is only about 0.1 percent. But potash and soda ash are such useful compounds that it is well worth the effort in extracting and purifying them—and remember that you can use the heat of the fire for other applications first. The reason that timber serves as a ready-packaged stash of these compounds is that over decades of time the tree’s root network has been absorbing, from a vast volume of soil, water and dissolved minerals that can then be concentrated with fire.

Both potash and soda ash are alkalis; indeed, the very term derives from the Arabic
al-qalīy
, meaning “the burned ashes.” If you now mix your extract into a boiling vat of oil or fat, you can saponify it, creating
your own cleansing soap. You can therefore keep the post-apocalyptic world clean and resistant to pestilence with just base substances like lard and ash, and a little chemical know-how.

This hydrolysis reaction is enhanced, however, if you use a more strongly alkaline solution: lye. This is where we return to slaked lime, calcium hydroxide.

You don’t want to use slaked lime itself for saponification because calcium soaps form a scum on water rather than a lovely lather. But the calcium hydroxide can be reacted with potash or soda so that the hydroxide swaps partners to produce potassium hydroxide or sodium hydroxide: caustic potash or caustic soda, both of which are traditionally called lye. Caustic soda is powerfully alkaline (it will readily hydrolyze the oils in your skin into human soap, so be extremely careful in handling it) and is therefore ideal for this crucial saponification process, making cakes of hard soap.
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Another alkali that is very easy to produce is ammonia. Humans, and indeed all mammals, get rid of excess nitrogen as a water-soluble compound called urea, which we excrete in urine. The growth of certain bacteria converts urea into ammonia—the distinctive stench of which you’ll be all too familiar with from poorly cleaned public restrooms—and so the crucial alkali ammonia can also be produced by distinctly low-tech means: fermenting pots of piss. This was historically a crucial process for the production of clothes dyed blue with indigo (traditionally the blue of jeans). We’ll return to the diverse uses of ammonia later.

Saponification of fat molecules will also give you another useful byproduct. The chemical component of the lipid that acts as the linker block grasping the three fatty acid tails, glycerol, is left behind after lard is transformed into soap. Glycerol is itself fabulously handy, and
can be easily extracted out of a lathery soap solution. The fatty acid salts of the soap itself are less soluble in brine than in fresh water, and so adding salt will cause them to sediment out as solid particles, leaving behind the glycerol in the fluid. Glycerol is a key raw material for making plastics—and explosives (which we’ll come to in Chapter 11).

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 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.