Gun cotton, also know as nitrocellulose, is a very interesting compound that can be made in the chemistry lab quite easily and is a good way to learn about the practical applications of simple chemical reactions.
What is gun cotton or nitrocellulose?
First, let's look at regular old 100% cotton. In this case, let's think of cotton balls that many people have sitting around their bathrooms. The cotton is made up cellulose fibers. Cellulose fibers are long chains of a compound called glucose (C6H12O6)n. Glucose is made by plants during photosynthesis (click for my page on photosynthesis) and is a circular carbon molecule with oxygen and hydrogens poking out like the spokes of a wheel. Glucose (called cellulose when it is grouped into long chains) burns quite well. Think of a log of wood, the fibers in the wood are similar to the fibers in the cotton, both are mainly made of cellulose. Wood, like cotton, burns well. But, using some simple chemistry, we can alter the cellulose so it will burn even better!
Fire requires three things: heat, fuel and oxygen. When burning a cotton ball, a match will provide heat, the cellulose fibers will provide fuel and the air will provide oxygen. It is the amount of oxygen in the air that causes the cotton to burn relatively slowly. By soaking the cotton in Sulfuric Acid and Nitric Acid, the hydrogens that were attached to the "spokes" of the carbon wheel are broken off and replaced by nitrogen and oxygen. Simply put, the spokes of the carbon wheel get more oxygen atoms stuck to them after a bath in strong acids. With all this extra oxygen, the cellulose can burn much more efficiently and will produce a quick, clean burning flame!
The name nitrocellulose gives a pretty good idea of the chemistry of the gun cotton. The "nitro" refers to the nitrogen groups that attach to the spokes of the glucose carbon wheel. Each of the nitrogens brings extra oxygens with it when it attaches. The "cellulose" of nitrocellulose refers to the cellulose fibers of the cotton. Hence the name "nitrocellulose".
Nitrocellulose is often found as a product called flash paper when 100% cotton paper is subjected to the same reaction. This paper is often used in magic shows as the magician is attempting to redirect the attention of the audience. It is available here and it is wiser to buy flash paper than to try to make your own!
How do you make gun cotton or nitrocellulose?
30ml Concentrated Nitric Acid*
70ml Concentrated Sulfuric Acid*
.7 grams 100% cotton
84 grams Baking Soda (Sodium Bicarbonate)
1000 ml Water (distilled if available)
Place a 250ml beaker inside an ice bath inside the fume hood. This is where you will mix the acids and soak the cotton.
Measure acids and carefully pour into the beaker in the ice bath - this will produce heat and dangerous vapors. Use caution
Using tongs, put .7 grams of cotton in the acid bath. Leave in fume hood for 15 minutes.
Prepare a 1.0M solution of sodium bicarbonate by dissolving 84 grams of baking soda in 1000ml of distilled water.
Fill a 500ml beaker with water. Remove cotton from acid bath with tongs and gently place in the water.
Put beaker in sink and turn on a slow stream of water so it pours into the beaker and allows the other water to pour out. This will allow the water to circulate and will wash off any excess acid. Rinse for 5 minutes.
Remove cotton and place into the 1.0M solution of sodium bicarbonate. This step will neutralize any remaining acids. Repeat this step multiple times with more baking soda if fizzing continues.
Remove cotton and allow to dry on a paper towel in a well ventilated area for 24 hours.
How do you store gun cotton?
Store in a sealed ziplock bag in very small quantities and use right away. Nitrocellulose is very volatile and should not be stored for any amount of time. Some people will store it in water and dehydrate it (dry it out) before they use it. If you purchase flash paper (buy it here), the paper version of gun cotton, it is usually shipped soaking wet with water for this reason.
*Concentrated acids are incredibly dangerous. Do not try this at home. Do not try this unless you are a trained professional and have the proper equipment and expertise. Beals Science will not be responsible for anyone who does not heed these warnings!*
Is gun cotton safe?
Nitrocellulose (gun cotton) burns very easily and could combust when exposed to static electricity, heat or flame. It should be used quickly and not stored. When lighting the gun cotton, use caution to not burn skin, hair or burn your house down!
Craig Beals made this video and tutorial to encourage other science teachers to share the wonders of science with their students. It was not made to encourage people to try this at home.