Almost every kid who's had a birthday party can relate to the fun of sucking on a helium balloon to hear yourself talk at an unnaturally high pitch. This happens because your vocal cords resonate at a frequency dependent on the speed of sound in a medium. Helium, being lighter than air, is less dense and allows a correspondingly higher speed of sound transmission. The compression of the sound waves therefore raises the pitch.
No, the little bit of helium in this ampule will not make the box float in air.
Comes in two varieties: regular and a special, low pressure gas ampule which will glow when ionized under high voltage. See colors at bottom of elements page