Since Ira Flatow's Science Friday show aired on NPR, I've been getting requests for additional information about where to find the metal salts that can be used to make colored fire. Here's a list of common sources of these metal salts. If the salts are in liquid form, simply soak pinecones or logs or whatever you are burning in the liquid and let the fuel dry before use. If the salts are solids, your best bet is to try to dissolve them in a bit of alcohol and then apply them to your fire fuel. You can use water, but expect a longer drying time.

Fire Color - Source

Green - Boric acid is probably your best source of "green". Boric acid most commonly is sold as a disinfectant in the pharmacy section of a store. Copper sulfate is another metal salt that produces green fire. You can find copper sulfate, usually diluted in liquid form, in products used to control algae in pools or ponds.

White - Magnesium compounds can lighten a flame color to white. You can add Epsom salts, which are used for a variety of household purposes. I usually see Epsom salts sold in the pharmacy section of stores for use as a bath soak.

Yellow - Your usual fire will be yellow already, but if you are burning a fuel that produces a blue flame, for example, you can turn it from green to yellow by adding sodium salt, such as common table salt.

Orange - Calcium chloride produces orange fire. Calcium chloride may be sold as a bleaching powder, with cleaners. It's usually easier to find as a road de-icing agent. Just be sure the calcium chloride isn't mixed with sodium chloride or else the yellow from the sodium will overpower the orange from the calcium.

Red - Strontium salts produce red colored fire. The easiest way to get strontium is to break open a red emergency flare, which you can find in the automotive section of stores. Road flares contain their own fuel and oxidizer, so this material burned vigorously and very brightly.

Purple - Purple or violet flames may be produced by adding potassium chloride to the fire. Potassium chloride is sold as lite salt or salt substitute in the spice section of the grocery store.

Blue - You can get blue fire from copper chloride. I am not aware of a widely-available source of copper chloride. You can produce it by dissolving copper wire (easy to locate) in muriatic acid (sold in building supply stores). This would be an outdoors-only type of reaction and not something I really recommend doing unless you have a little chemistry experience... but if you're determined, dissolve a piece of copper in a solution of 3% hydrogen peroxide (sold as a disinfectant) to which you have added sufficient muriatic acid (hydrochloric acid) to make 5% HCl solution.

Do you know of other sources of metal salts that can be used to color fire? If so, please add your comments in response to this post.

On July 6, 1885, Louis Pasteur tested his rabies vaccine on Joseph Meister. Meister was a nine year old boy who had been badly bitten by a rabid dog and was facing the near certainty of developing the disease himself. Pasteur had been developing a vaccine for rabies from rabbits. He grew the virus in rabbits and removed the infected spinal tissue. The tissue was then dried out to weaken the virus. The weakened virus was injected into the boy and he never developed the disease. This new treatment would save many people from a common and potentially fatal disease.

Joseph would grow up to become the caretaker of the Pasteur Institute until his death in 1940. Find out what else occurred on this day in science history.

June 5^th is the birthday of John Howard Northrop. Northrop was an American biochemist who perfected a method to isolate and crystallize enzymes. This allowed him to examine the chemistry and structure of several enzymes and earned him part of the 1946 Nobel Prize in Chemistry. Using these methods, Northrop was first to isolate a bacteriophage or anti-bacterial virus and identify it as a nucleoprotein.

Northrop's research greatly advanced the understanding of the chemical nature of enzymes and proteins. Find out what else occurred on this day in science history.

Happy 4th of July! Here's a project for you to try today: make a smoke ring cannon. This is a tube that you fill with smoke that has a hole at one end. You squeeze the tube and the smoke escapes through the hole as a smoke ring. This works great with smoke bombs, but you can make smoke rings in fluids besides air. Try filling the smoke cannon with colored water (use tub tints, food coloring, or paint), fill a tub or sink with water, and make 'smoke rings' in the water.

Smoke Cannon Materials

• Potato Chip Tube (I used a plastic one, but the cardboard ones work fine.)
• Knife or Scissors
• Source of Smoke

Make and Use the Smoke Cannon

1. Eat the chips.
2. Cut a hole in the center of the bottom of the potato chip tube (mine is about an inch across).
3. Remove the lid of the tube.
4. Covering the hole with your hand or lid, invert the smoke cannon over a source of smoke until it is full of smoke.
5. Seal the tube with the lid.
6. To make a smoke ring, gently squeeze the tube.

You can make a super-sized smoke cannon by using a much larger cylinder, such as a bucket or trash can. Cover the open end of the trash can or bucket with heavy plastic sheeting, which you can secure with tape or a bungee cord. Thump the plastic surface to form the smoke rings.

July 4^th is the American Independence Day typically celebrated with firework displays. In 2005, NASA arranged their own fireworks display by purposely ramming part of their Deep Impact probe into Comet Tempel 1. The Deep Impact mission was designed to fly in close to a comet and launch a projectile into the core while the flyby satellite analyzed the ejected debris. This would give scientists a glimpse of the the early makeup of the Solar system when comets were believed to be formed.

The comet contained many expected materials such as water ice and silicates, but also contained unexpected materials. Carbonates and aromatic hydrocarbons were also found. The data will affect the theories about how planets are formed.

Find out what else occurred on this day in science history.

Of course! You need to get primed for the big fireworks displays tomorrow, so get started with firecrackers. Now... the thing about this project is, the more gunpowder you use, the bigger bang you will get. Do have fun, but don't go overboard. If you're a diehard do-it-yourselfer, you can make your own gunpowder. Alternatively, you can collect the powder from toy gun caps. I've designated the remainder of the day "4th of July Eve" so start celebrating!

July 3, 1969 was supposed to be the day the Soviets launched their new N1 rocket. The N1 was their largest rocket design and their answer to the United States' Saturn V rocket. It was just under 350 feet tall. 30 engines in the first stage gave a thrust of almost 10 million pounds and could lift 95 tons of cargo. At least, that was the plan.

Shortly after liftoff a loose bolt fell into the fuel pump and immediately destroyed the pump. 29 of the 30 engines automatically shut down, stalling the rocket. 23 seconds later, the 1,780 tons of liquid oxygen and 680 tons of kerosene fuel exploded, destroying the rocket and the launchpad. This spectacular explosion was the largest rocket explosion to date.

The N1 design never successfully launched and crippled the Soviet efforts to place a man on the moon. Find out what else occurred on this day in science history.

Annette Heist of NPR asked me if I'd join her for Science Friday on July 3rd to talk about science projects for kids, especially 4th of July science projects. It sounds like fun! If you'd like to listen, tune in to NPR's (National Public Radio) Science Friday around 2:15 pm EST / 1:15 CST.

July 2^nd is the birthday of Hans Bethe. Hans Bethe was a German-American physicist who was awarded the 1967 Nobel Prize in Physics for describing how stars create their energy. He was in a good place to work out ideas in atomic and nuclear physics when he worked in the theoretical division of the Manhattan Project to build America's atomic bomb. He was part of the team that calculated the critical mass necessary for a chain reaction and later worked on the implosion method to start that chain reaction.

After the war, President Truman announced the hydrogen bomb project and Bethe joined the project but hoped it would prove an impossible task. His personal feelings against atomic and thermonuclear weapons showed when he joined Einstein's Emergency Committee of Atomic Scientists against nuclear testing and the arms race. He also played a role in the eventual ban on atmospheric testing and the SALT I Anti-Ballistic Missile Treaty.

Find out what else occurred on this day in science history.

You only need two non-toxic ingredients to make smoke bombs for the 4th of July. I've got a video tutorial for you or you can use the written step-by-step smoke bomb tutorial. Have fun!