The Knowledge: How to Rebuild Our World From Scratch (16 page)

BLAST FURNACE FOR SMELTING IRON. THE ORE, FUEL, AND FLUX ARE FED IN AT THE TOP, AND AN INTENSE STREAM OF HOT AIR IS FORCED UP THE STACK FROM THE BOTTOM.

The innovation that really made possible the later stages of the Industrial Revolution was a means for easily transforming blast-furnace pig iron into steel. In terms of carbon content, steel lies in between pure wrought iron (usually less than .01 percent carbon) and brittle pig or cast iron (3–4 percent carbon): from about 0.2 percent carbon for tough steel for machine gears or structural members, to about 1.2 percent for particularly hard steel for ball bearings or the cutting tools of your lathes. So how do you decarbonize pig iron?

The Bessemer converter is a giant pear-shaped bucket, lined with refractory bricks and mounted on pivots so it can be tipped. The vessel is charged with molten pig iron, and then air is pumped in through holes in the bottom, not unlike the action of a bubbling aquarium
aerator. The excess carbon reacts with the oxygen and escapes as carbon dioxide gas, and other impurities are also oxidized and scrubbed out into the slag. One lucky outcome is that as the carbon burns it releases enough heat to keep the iron molten throughout.

The difficulty is that it is hard to judge the operation accurately enough to remove almost all of the carbon, but leave just under 1 percent. The trick for nailing the final composition, obvious in retrospect, is to run the conversion long enough that you are sure absolutely all of the carbon has been removed, and then simply mix exactly the final percentage you want back into the pure iron. This Bessemer process was the first method in history for cheaply mass-producing steel, and you’d want to leapfrog back to this point as quickly as you can.

While iron and steel are the celebrated building stuff of the modern industrialized world, humble glass, so easily overlooked (or at least looked through), has also been critical in our progression. Glass, one of the first synthetic materials to be made by humankind, was invented in Mesopotamia, the cradle of the first cities, some time in the third millennium BC. We’ll see in a bit how glass, and its unique combination of essential properties, forms the linchpin of science. But let’s start with the fundamentals of how to make the stuff.

You probably know that glass is made from molten sand, or more precisely from purified silica (silicon dioxide). But simply chucking handfuls of sand into a fire won’t yield you any results, other than perhaps snuffing your fire. The problem is that silica has an exceedingly high melting point, at around 1,650°C. This is far beyond the capability of a simple kiln, and so just knowing the main constituent in glass doesn’t help you actually make it. Glass is sometimes produced
naturally: if you dug around in the sand of a desert you might be lucky enough to unearth curious long hollow tubes of fused silica, often resembling the complex branched root system of a tree. A structure like this is called a “fulgurite,” or “thunderbolt stone,” and is created when lightning strikes dry sand. The electrical current surges underground and produces temperatures high enough to fuse silica grains together into a glassy tube.

Since you can’t directly harness the power of lightning, in order to manufacture glass you must be able to lower the melting point of silica to within the reach of a kiln, using a suitable flux additive. Either potash or soda ash works perfectly well as a flux for silica in glassmaking, but as we’ll see in Chapter 11, with a little application of chemistry, soda is much easier to produce in bulk. So the vast majority of glass made today for windowpanes or bottles is soda-lime glass—a solution of soda and lime dissolved in sand that freezes at everyday temperatures.

A ceramic crucible, fashioned from fired clay, is filled with silica grains and your soda crystals. In the heat of the kiln, the sodium carbonate decomposes (giving off carbon dioxide) and dissolves in the silica, lowering its melting point enough to successfully produce glass at the temperature of the kiln. The carbon dioxide given off, combined with oxygen and nitrogen trapped in the initial mixture, forms a bubbly, frothy melt. So a very hot kiln that keeps the molten glass very runny should be used and the crucible left inside long enough to allow these bubbles to escape and produce a clear glass. Unfortunately, glass manufactured from just silica and flux dissolves in water, severely limiting its usefulness. The solution is to use a second additive in the crucible to render the glass insoluble: quicklime—the calcium oxide we encountered in the previous chapter—works well for this.

Silica, the base material for glass, makes up more than 40 percent of the Earth’s mantle and crust—it is by far the most abundant
compound in the rocks of our planet. But silica is often mixed in with many other things (including metals—silica is the main component of the slag thrown away after smelting), and to make a clear, colorless glass you want it to be as pure as possible. The brownish tint to much sand, for example, is due to iron oxides, and these will tint the resultant glass green—fine for a wine bottle, irritating for a window or telescope. The best source for clear glass is a bright white sand, or other uncontaminated silica like the white quartz pebbles used for the famous Venetian “crystal” glass or the flints picked out of chalk for English “
lead crystal” glass (both are technically misnomers, as all glass has its atoms arranged in a totally disordered, noncrystalline mess.)

Of course, there will be an enormous amount of glass left behind by the old civilization that can be salvaged. That which has been preserved whole can be reused, and smashed glass can be cleaned and remelted. Indeed, glass is one of the most easily recyclable materials today. It is simply melted in a furnace and then reformed, and this can be repeated time and time again without any deterioration of the material (unlike plastics, for example). But you’ll need to know the necessary recipe for making glass from scratch later in the civilization-recovery process, or if you’re shipwrecked on a deserted island. In fact, a tropical beach might be pretty much the ideal location to collect the three raw materials needed for clear, high-quality glass: iron-free bright white sand, seaweed to extract soda ash, and seashells or coral to calcine into quicklime.

Glass in its molten state can be poured straight out of the crucible and into a mold. But a far more useful manufacturing process exploits one of its curious attributes. Glass has the unusual property that it possesses no single melting point. Instead, the viscosity of glass (or its runniness) varies greatly over a range of temperatures, and so you can work with the material when it’s in a sweet spot of being pliable but not too runny—and this allows for glassblowing. Daub a glob onto the end
of a clay or long metal pipe and you can force air in to inflate the glass, either turning it in open air to work into the desired shape, or blowing into a mold to rapidly manufacture objects like bottles.

Windows are vital today for illuminating our homes and skyscrapers, allowing sunlight to flood into our artificial caves while providing a barrier to keep out the elements. The Romans were the first to glaze their windows, using small pieces of cast glass, while by the end of the first millennium AD, Chinese windows were still covered with paper, made translucent with oil. For many centuries, windowpanes were first blown and then spun flat while still soft—the distinctive dimple in the middle, still seen in the windows of old country houses or pubs, is where the glassblower’s pipe was detached. Today, large, perfectly smooth window panes are made by pouring glass onto a bath of molten tin, where it floats and spreads out into a slick of uniform thickness before cooling and setting. But beyond windows, glass will offer other fundamental uses during recovery in the post-apocalyptic world.

The primary attribute of glass that makes it such a handy material for windows is, of course, that it is transparent. This in itself is a rare material property. But, in fact, glass offers a whole combination of crucial attributes that are not found in any other substance. This means that glass is utterly critical for science: studying natural phenomena, measuring their effects, and devising ever more capable technology from this knowledge. The barometer (a pressure indicator) and thermometer, for example, were the first two scientific instruments invented, and both operate by displaying changes in the level of a column of liquid. It would be impossible to see these fluctuations without the clear, hard material that is glass.

Microscope slides, too, rely on the fact that thin samples can be stuck to a substrate that lets light through. Glass is also pretty strong, and can make airtight enclosures capable of containing a vacuum. Vacuum tubes are required for the generation of X-rays (see Chapter 7 on
medicine), and were critical to the discovery of electrons and other subatomic particles. Airtight glass bubbles are also central to the working of a filament light bulb or fluorescent lamp: holding a particular internal atmosphere while allowing the generated light to shine out.

As well as being transparent, heat-resistant, and strong enough to make thin-walled vessels, glass is also largely inert. And this has been critical for every aspect of chemistry research. Glass can be molded or blown into all the varied forms of laboratory apparatus: test tubes, flasks, beakers, burettes, pipettes, pipes, condensers, fractionating columns, gas syringes, measuring cylinders, and watch glasses. It’s hard to see how chemistry could ever have progressed without access to a material that is both inert and see-through, allowing us to watch what happens in a reaction without tainting it.

But perhaps the greatest gift of glass is that it can be used to control and manipulate light itself. And this allows us not only to contain little pockets of nature to study in isolation, but to extend our very senses.

The Romans were masters of glassmaking, and noticed that a glass globe appeared to magnify objects behind it. But they never made the next conceptual step: to grind a lump of glass into a curved shape, creating a lens. A lens relies on the principle of refraction, where the path of a light ray is bent as it passes from one transparent medium to another. This can be seen by poking a straight stick into a pond—the stick appears to be kinked below the waterline. This is due to light rays refracting at the lake’s surface, the interface between the water and air. A piece of glass formed into a particular shape, a lenticular form with a bulging, bowl-shaped curve on both sides—symmetrically convex—controls the refraction of light rays passing through it. Light arriving near the outer rim of the lens is deflected inward greatly because it hits the surface at a large angle; light passing nearer to the center is bent to a lesser degree; and rays lancing right through the middle of the lens hit its curved surface head-on and so continue straight. The
outcome of this is that you have brought all the light paths together at a single point, the focus. This is the principle of a magnifying glass.

The first optical technology was spectacles, appearing in Italy around 1285 with convex lenses to help people with farsightedness, which often develops later in life, when your eyes struggle to focus on nearby objects. Correction of nearsightedness demands a concave lens, and correctly grinding a puck of glass in this opposite way—so that its two faces curve in toward the middle and light rays are instead diverged—is a little trickier.

The real breakthrough comes with the realization that if lenses can apparently enlarge objects viewed through them, a carefully arranged combination of lenses can allow you to see far into the distance—the essence of the telescope. This gadget was first used by ship captains, but was soon pointed toward the heavens to initiate the great revolution in our comprehension of the cosmos and our place within it. But glass lenses also allow you to magnify the very small, and the microscope is absolutely indispensable for understanding microbiology and germ theory, examining the structure of crystals and minerals, and improving metallurgy.

One of the first artificial substances synthesized by humanity more than 5,500 years ago, glass has enabled us to investigate nature and construct new technologies, from the first pair of reading spectacles to the Hubble Space Telescope. Of the six instruments crucial to the development of the modern scientific enterprise in the seventeenth century, all of which would be indispensible in rediscovering the world after an apocalypse—pendulum clock, thermometer, barometer, telescope, microscope, and vacuum chamber with air pump—all but one of them, the pendulum clock, rely utterly on the unique combination of properties offered by glass.

It’s astounding to think that the telescopes extending our eyesight throughout the cosmos and the microscopes exploring the minute
structure of matter all come down to a simple curved lump of sand. Glass, in a very literal sense, changed our view of the world. It will be crucial for a successful recovery of civilization after the Fall, both as a building material and as a critical gateway technology for conducting science. The thermometer, barometer, and microscope are all also crucial for examining the state of the human body, and so it is to medicine that we will now turn.