Science Buddies: "Ask an Expert"

Hi. We are doing the Getting a Bang out of Your Breath Spray experiment. We built the apparatus using a gas grill igniter. It had two leads. We followed the instructions. The only thing we did differently was that we nailed the film cannister lid to the wood block. We used a hot glue gun as well as epoxy cement.

When we pressed on the igniter, it created a spark. We then used Binaca spray which has SD Alcohol 38B. We sprayed 2 squirts quickly and attached the cannister to the lid. But, we can't seem to create an explosion. We know the igniter is working because we see a spark. At best, when the cannister is not firmly placed on the lid, we get a small fire and the lid falls off the wood. We also tried Aqua Net hairspray, suede and nubuck cleaner (which has propane), and stainless steel cleaner. Nothing seems to work. What are we doing wrong? Please help. Our experiment is due soon.

[Administrator note: Project: https://www.sciencebuddies.org/science- ... #procedure]

Hi Seanmvienghou,

The amounts of fuel and air inside the canister are critical for creating an explosion. Two squirts of breath spray may be too much fuel. You may want to try again with one squirt or you might try changing the duration of the spray. Also, the project procedure (Launching the Canister, step 7) suggests taking the canister off after a failed attempt to add some air and let some fuel out. Reattach it to the base and try again.

Another possibility is that the canister assembly leaks and doesn't develop enough pressure inside after the fuel ignites. Make sure that all the holes in the canister lid are sealed with glue as shown in the procedure. And the lid must be firmly snapped onto the canister before setting off the spark.

I hope this helps. Please ask again if you have more questions.

A. Norman