I am sometimes asked how I come up with the activities for my books. Here’s a story to illustrate the process.
In general, an activity begins with an interesting tidbit of information, and a thought of something it might cause in the real world. Then come rounds of tests to try to find a way to make it work.
I came across the information that human skin and hair is more acidic than dog skin and hair. Brilliant! We’ll test skin pH, I thought. Purple cabbage is the easiest household way I know for testing pH. So I boiled some purple cabbage leaves, and rubbed q-tips on my neck and the neck of a very patient Zorro.
Unfortunately, I couldn’t get Zorro’s skin oils to mix with the cabbage water enough to test…
I also read that it is important to use dog shampoo instead of human shampoo. Brilliant again! I thought. I bet dog shampoo is less acidic and we could test the pH of the shampoos.
In purple cabbage, a pale purple indicates neutral and the color moves toward pink/red as it gets more acidic and towards blue/green as it becomes more basic. I wasn’t expecting a huge color difference, as both humans and dogs fall into the highly technical category of “slightly acidic.”
You can see my results above. They are all over the place. Certainly one of the human shampoos (Dove) was much more acidic than everything else. But the least acidic, although the color isn’t as clear in this picture, was also for people (an old hotel give-away). The dogs were somewhere in between. At the time, I thought perhaps purple cabbage wasn’t discriminatory enough (or that “specially formulated dog shampoos” were a crock).
Later, though, I asked Brenda DuVal, a chemist with John Paul pet products, about the pH of dog shampoos. She explained that, when it comes to pH, skin isn’t the deciding factor. That honor belongs to their eyes. Dog shampoo is supposed to be formulated so it won’t sting if it gets in their eyes.
So pH testing went in the “wouldn’t that have been fun” folder, and I moved on to more successful activities that DID get in the book.