Excerpted with permission from The Chemistry of Alchemy: From Dragon's Blood to Donkey Dung, How Chemistry was Forged, by Cathy Cobb, Monty Fetterolf and Harold Goldwhite. Available from Prometheus Books. Copyright © 2014.
The liquids from this demonstration can be disposed of down the sink, but you’ll want to keep the golden penny taped inside a notebook.
In this demonstration we’ll perform a transmutation! Or at least that’s how the alchemists would see it. The Alexandrian artisans saw it as making false gold, but the practical artificer and the alchemist often interpreted the exact same chemistry in quite different ways.
So here we go.
First, please put on safety glasses.
Find a new US penny, one with a shield on the reverse side (tails) instead of the Lincoln memorial; that is, from 2010 or later. It’s best if your penny is shiny and new, but even if it looks clean, clean it by soaking it in a salt-and-vinegar solution. If you can’t find a post-2009 penny, a post-1982 penny will do, but they are a harder to clean and don’t seem to work quite as well.
Set out a shallow bowl of water to slide the penny into when you take it off the heat. The coin will be hot enough to make a fine sizzle when it hits the water. Check to see that your exhaust fan is providing adequate ventilation by boiling water and making sure the steam is being pulled away from you.
Take a cast-iron skillet, put it on a burner, and set the burner to two notches below the maximum setting. Please note we don’t recommend a stainless-steel skillet (it may warp with continued strong heating), and we don’t recommend a nonstick skillet because the high heat may degrade the coating into unfriendly chemicals you don’t want to breathe. In addition, please realize this is a sacrificial skillet: after you have used it for demonstrations, you can’t use it to cook food.
But we think it’s worth the sacrifice.
After the skillet has warmed on the burner for around one to two minutes, drop the penny into the center of the pan and wait. After about five minutes, you will see a wave of purplish color creep over the surface of the penny. Keep waiting. After another two to three minutes, the purple color should give way to a spreading golden sheen. Wait until the golden color has spread over the entire surface (about another half minute) and then slide the penny off into the water. The entire time for the penny on the burner should be seven to eight minutes. If the burner is too hot or you wait too long, you may ruin the penny and an upcoming demonstration.
Turn off the burner and set the skillet on a heat-resistant surface (a cooled stovetop burner or an inverted pan). If all has gone well, the surface of the penny should have a beautiful golden sheen. Compare it with an untreated penny for full effect.
If you saw the purple wave but the penny didn’t turn gold, you need to leave it on the heat longer after the wave. If you didn’t get a purple wave, you need to try a slightly higher heat.
What’s going on?
It turns out zinc and copper, when heated at a high temperature, fuse to make an alloy, brass, that is golden in color. The Egyptian artisans obviously didn’t have pennies, but they did know about an ore that colored the copper, which we now know contains zinc. Post-1982 pennies, it turns out, contain 97.5 percent zinc and 2.5 percent copper, which is perfect for our purposes.
But this isn’t a very authentic demonstration. We can make it a bit more authentic by using zinc and copper samples. Alternatively you can use the zinc-coated fasteners found in hardware stores, as long as they are truly zinc-coated (check the package).
If you have bare copper wire (no insulation), your copper sample is ready. If your wire has insulation, remove the insulation with wire strippers or by shaving it off with a small, sharp knife. Use work gloves and shave away from your body. Put a few chunks of zinc or the zinc-coated fasteners into a crucible and nest a small coil of copper wire in with the zinc (it should touch the zinc). Add a few chunks more of zinc on top. If your crucible has a cover, put the cover on or use a watch glass as a cover. Place the entire assembly (covered crucible with the zinc-surrounded copper wire) in the cast-iron skillet and set the burner on whatever heat worked for the penny. Give the material in the crucible about six minutes to form the alloy and then take the cast-iron skillet with the crucible off the burner and place it on a heat-resistant surface. Allow about fifteen minutes to cool. When you carefully uncover the copper in the crucible, you should find it has a golden surface.
Does it look exactly like gold? No. But most people the artisans served had never seen real gold up close, so it probably looked fine to them. In addition, a short trip to the jewelry store will demonstrate that not all gold looks alike. White gold is different from 24-karat gold, and there are alloys called rose gold and yellow gold, too. And they all glitter.
The name the old alchemists would have used for the above process, besides transmutation, would have been calcination. Calcination usually means to heat something strongly in air, but unfortunately most alchemists didn’t walk around with a dictionary of alchemy, and, as far as we know, there was no international meeting to standardize alchemical terminology, so calcination meant other things, too. For instance, dissolving a substance could be called calcination. And while calcination generally results in a reaction, simple melting or evaporation can also be the outcome. So there you have it: one word; many meanings.
Welcome to alchemy.
The alchemists loved distillation, and for good reason. Distillation is a method for separation, one of the alchemists’ primary goals: they strove to separate and isolate the “spirit” or the “essence” of a substance so it could be recombined with a body that would result in gold. They had many other methods for separation as well, but distillation was the workhorse of alchemy.
Distillation accomplishes separation based on a difference in boiling points or volatilization temperatures for different substances. In distillation, a mixture is heated until some part of it goes into the gas phase. The gas phase is then separated from the rest of the mixture by means of a tube or an arm that leads the gas away. Imagine a still you’ve seen in movies or cartoons for making moonshine, and you’ll know what we mean. Still stands for distill, and in this demonstration you will build a still and test it with the problem of the ancient Alexandrian Egyptians: extracting fresh water from salty.
You’ll need a large beaker or a cooking pot to use as the still pot (the bottom of the still), a clay flowerpot, a 5-foot length of copper tubing, modeling clay, and two receptacles (jars or cups will do). The tops of the still pot and the flowerpot should match in size, if possible, but if not, the still pot should be a bit larger than the flowerpot. The copper tubing has to be able to fit through the hole in the bottom of the flowerpot.
Fill the still pot about half-full with water, add about two tablespoons salt, stir, and then use swimming-pool salt test strips to measure the salinity of the water.
The test strips are marked off in units of ppm, which stands for parts per million, and is a measure of how concentrated, how salty, the water is. The saltwater we made measured between 3,000 and 4,000 ppm salt on the test strip, but you don’t have to match this exactly. As long as the water is fairly salty and you know the beginning concentration, you are fine. After measuring the salinity, place the still pot in the cast-iron skillet on the stove.
Next, invert the flowerpot and attach it to the still pot with modeling clay. Form an angle in the top and bottom of the copper tubing so it will fit into the top of the inverted flowerpot and curve down into the receiving vessel, again as shown in the picture at the beginning. Seal the flowerpot to the copper tubing with modeling clay, make sure your setup is stable, turn the heat to a couple of notches above medium, and then wait.
As the saltwater heats up in the still pot, the copper tubing will heat up, too, and, in fact, can become quite warm, so be careful. The tubing heats up because the steam entering the tubing gives up its heat to the copper as the steam condenses, which is one reason copper is a good choice for tubing.
Eventually the condensed water will begin dripping into the receiving flask. When you have collected a reasonable amount of water, swap the filling receptacle with an empty one and test the salinity of the water you’ve collected with your pool test strips. When we tested our distilled saltwater, there was no change in the test strip; in other words, any remaining salt was below detectable limits. You will probably see the same thing, that is, no salt left in the water, but if any salt is left, it will be well below the amount present at the beginning of the distillation.
Fresh water for Alexandria, and onward to the East!