 In the earlier segment, when we were looking at the spectra tube, we were using a high-voltage electricity to excite those electrons in hydrogen. What we know is that we can make fireworks. We can take salts, like lithium chloride, lithium nitrate, potassium, sodium, and we can make a different color by putting them in a fire. So if we take lithium chloride, for example, and put it in the flame, we get a very characteristic pinkish-red color. I want you to jot down what that color looks like to you. Is that color due to the lithium, or is it due to the chlorine ion? And we can make that decision by trying lithium nitrate. And what do you think will happen if it's due to the lithium? So let's try it and see. If the color is the same for lithium chloride and lithium nitrate, then what do you think is the ion that's producing the color? And that's pretty obvious, isn't it? It's the cation.