This instructable shows an easy way to make nitrocellulose (also known as gun cotton). Nitrocellulose is a fun compound that is safe to handle, burns very fast, and can be used in explosive mixtures like smokeless powder and APNC (acetone peroxide and nitrocellulose), and in fuses, rockets, whatever you can think of.
This isn't the best way to make nitrocellulose. If you want super good nitrocellulose mix concentrated sulfuic acid with concentrated nitric acid 2 to 1 by volume, cool the solution to below 25 degrees F (ice and salt works), then slowly add cotton and let it soak for 12 to 24 hours while keeping the ice fresh. Then clean it with cold water (no baking soda) until there is no acid left. Nitrocellulose made this way can be detonated by hitting a pinch of it with a hammer.