There can be many reasons why an activity didn't work. Make sure you have used the correct materials, followed all the instructions and have not substituted any items. If you are doing an activity that involves batteries, check to see if the batteries are fresh. Try the activity again, just in case you missed a step or didn't follow the instructions. Because our books are published in different countries, formulas or strengths of certain items may not be the same. An example of this was when the manufacturer of the laxative changed their formula so that the color changing part of the experiment no longer worked.