One of the things we are interested to know if there is any chemical reactions between two compounds. One of the ones I have is sodium carbonate, a transfer of it in a small test, you just have a little bit of it. And today I am going to add a few milliliters of tremolo hydrochloric acid and then you realize that there is a reaction going on, so fizzy. So what it means is there is some gas for, I need to find out the nature of this gas. What is it? I am going to put burning explained inside the test, you will see what happens. So the flame went off. So that way we can identify what kind of gas is it that put the flame on. And that is what you have to figure out.