For several minutes, it seemed an innovative "great big science class'' would end not with a bang but a whimper in Dunedin yesterday, when a liquid nitrogen "bomb'' failed to explode.
The "bomb'', in a 44 gallon drum, was supposed to send 4000 ping pong balls flying at the Forsyth Barr Stadium, marking the end of the science class, in which more than 1100 Dunedin school pupils participated.
The event was a fun science education show linked to the week-long New Zealand International Science Festival, whose main programme starts in Dunedin today.
The science class was supposed to culminate with the planned explosion at 12.20pm, and boiling water was duly poured on to a plastic soft drink bottle filled with liquid nitrogen.
The theory was that as the nitrogen warmed, the rapidly expanding gas would smash the bottle and propel the ping pong balls skyward.
Excited school pupils sat safely in a grandstand, and made a noisy countdown from 10, but when they reached zero, nothing happened.
A second countdown was also fruitless. Festival director Chris Green then used a microphone to apologise and promised the experiment would be repeated at schools.
But before Mr Green could finish, the drum exploded loudly.
Yesterday's event was organised by the University of Otago's psychology and chemistry departments and the science festival.
Organisers said it was the biggest science class of its kind conducted in New Zealand and Australia.
It was also believed to be the largest number of ping pong balls fired skyward by nitrogen gas in New Zealand.
Earlier, for about 45 minutes, pupils from Logan Park High School and Tahuna Normal Intermediate School lined up or moved around the stadium's playing pitch, simulating the activity of neurons in the brain.
University psychology Teaching Fellow Dr Celia Lie, who co-ordinated the brain cell class, hoped the pupils had gained some "basic understanding'' of the brain and also appreciated that "sleep is good for the brain''.
The science festival continues at the university's St David lecture complex over the weekend and will include a free-entry science expo on Saturday from 10am-4pm and Sunday from 9am-12pm.
