Since you’ll want your first experiment to be authentically messy, we’ll start with detox. Detox footbaths have been promoted uncritically in some very embarrassing articles in the New York Daily News, the Telegraph, the Mirror, The Sunday Times (London), GQ magazine, and various TV shows. Here is a taster from the New York Daily News: it’s a story about Ally Shapiro, a fourteen-year-old who went to a “detox” center run by Roni DeLuz, author of 21 Pounds in 21 Days: The Martha’s Vineyard Diet.

“The first day I did it,” says Shapiro, “the water was completely black by the end.” By day three, twenty minutes in the footbath generated a copper-colored sludge—the color of the flushed buildup from her joints related to arthritis, DeLuz explained. The hypothesis from these companies is very clear: your body is full of “toxins,” whatever those may be; your feet are filled with special “pores” (discovered by ancient Chinese scientists, no less); you put your feet in the bath, the toxins are extracted, and the water goes brown. Is the brown in the water because of the toxins? Or is that merely theater?

One way to test this is to go along and have an Aqua Detox treatment yourself at a health spa, beauty salon, or any of the thousands of places they are available online, and take your feet out of the bath when the therapist leaves the room. If the water goes brown without your feet in it, then it wasn’t your feet or your toxins that did it. That is a controlled experiment; everything is the same in both conditions, except for the presence or absence of your feet.

There are disadvantages with this experimental method (and there is an important lesson here—that we must often weigh up the benefits and practicalities of different forms of research, which will become important in later chapters). From a practical perspective, the “feet out” experiment involves subterfuge, which may make you uncomfortable. But it is also expensive: one session of Aqua Detox will cost more than the components to build your own detox device, a perfect model of the real one.

You will need:

• One car battery charger
• Two large nails
• Kitchen salt
• Warm water
• One Barbie doll
• A full analytic laboratory (optional)

This experiment involves electricity and water. In a world of hurricane hunters and volcanologists, we must accept that everyone sets their own level of risk tolerance. You might well give yourself a nasty electric shock if you perform this experiment at home, and it could easily blow the wiring in your house. It is not safe, but it is in some sense relevant to your understanding of MMR, homeopathy, postmodernist critiques of science, and the evils of big pharma. DO NOT BUILD IT.

When you switch your Barbie Detox machine on, you will see that the water goes brown, due to a very simple process called electrolysis; the iron electrodes rust, essentially, and the brown rust goes into the water. But there is something more happening in there, something you might half remember from chemistry at school. There is salt in the water. The proper scientific term for household salt is “sodium chloride”; in solution, this means that there are chloride ions floating around, which have a negative charge (and sodium ions, which have a positive charge). The red connector on your car battery charger is a “positive electrode,” and here negatively charged electrons are stolen away from the negatively charged chloride ions, resulting in the production of free chlorine gas.

So chlorine gas is given off by the Barbie Detox bath, and indeed by the Aqua Detox footbath, and the people who use this product have elegantly woven...