Whistle mix is a general term to refer to any pyrotechnic composition that emits a whistling sound when pressed into a tube and ignited. It is used as a rocket propellant, particularly in small bottle rockets. Whistle mix tends to be fast burning and brisant; therefore it is also used as burst charge in shells.
A typical whistle mix is made from 70% potassium perchlorate and 30% sodium benzoate, measured by weight. The fuel in most whistle compositions is a salt of an aromatic hydrocarbon. Compositions with chlorates and gallates were used historically, but have now been abandoned as prone to accidental ignition.
Whistle compositions tend to be particularly sensitive. To achieve the whistling behavior, the composition must be formed into a solid grain; it otherwise burns too rapidly and just explodes. The composition is typically compressed using an arbor or hydraulic press. Ramming with a mallet (which is acceptable for many other compositions) may result in an explosion.
Famous quotes containing the words whistle and/or mix:
“The dusk runs down the lane driven like hail;
Far off a precise whistle is escheat
To the dark; and then the towering weak and pale....”
—Allen Tate (1899–1979)
“I will go back to the great sweet mother,
Mother and lover of men, the sea.
I will go down to her, I and no other,
Close with her, kiss her and mix her with me.”
—A.C. (Algernon Charles)