Loud whistling rockets can be made with this. The author of the text this composition was taken from used it in nozzle-less whistling rockets. The rocket casings were 3/4 inch inner diameter, and 3.25 inch length. The fuel grain ended 1/8" from the rear end of the motor tube.

Method:

1. Mix the iron oxide with the potassium benzoate and mill this mixture until a very fine powder is obtained.
2. Melt the petroleum jelly in a beaker on low heat. Turn the hot plate or stove off. Make sure no sources of heat or sparks are present before proceeding with the next steps.
3. While stirring, add 5 parts of toluene to each part of petroleum jelly by weight. Lacquer thinner can be substituted for toluene when pure toluene is not available. Continue stirring until the petroleum jelly has completely dissolved in the solvent used.
4. Add the petroleum jelly to the potassium benzoate/iron oxide mix and stir the mixture until it becomes homogenous.
5. Then, slowly add the potassium perchlorate while stirring continuously with a wooden spoon for several minutes until homogenous. At this point, the mixture usually has a consistency of thick soup and the beaker is warm to the touch. If the mixture seems too dry or thick, extra toluene or lacquer thinner can be added at this stage.
6. Spread the composition out in a layer about 1/2" thick on kraft paper over newspapers to dry overnight. It is important that the mixture has thoroughly dried before pressing motors. A slightly damp mix can cause some shrinkage of the propellant grain over a period of days or weeks, causing the rocket to explode when ignited.
7.  When the composition has dried overnight, carefully run the mixture through a 20-mesh sieve twice and store in a paper container so that trace amounts of solvent can evaporate. After several days, the mix is ready to press.

NOTE: Whistle rockets must be made in the same way as a standard firework whistle, in the sense that it must be pressed very firmly for it to produce a whistling effect. The catalyst can be any metal oxide, though the usual ones used are titanium dioxide, copper oxychloride, and red iron oxide.

DANGER: Whistle compositions should NEVER be rammed. They must be pressed or an explosion may result.