The students sitting on the steps of the Franklin Institute wondered what happens when several gallons of dish-soap solution are dumped into a trash can full of liquid nitrogen.

They didn't wonder long.

An explosion of bubbly, foamy suds sprayed the kids from Russell Byers Charter School and Cristo Rey Philadelphia High School, bestowing the kind of OMG moment that the fifth annual Philadelphia Science Festival aims to give all participants.

Thursday's news conference offered a sneak peek of the nine-day festival, set for April 24 to May 2. Hundreds of the region's parks, libraries, universities, museums, eateries, and pubs will join the institute to host more than 100 events, all designed to stoke interest in science and technology. Many events are free; tickets for the rest are on sale at www.philasciencefestival.org.

"Science makes this city great," said Larry Dubinski, president and CEO of the Franklin Institute. "We want to inspire the next generation of scientists."

The festival instills "contagious curiosity," added Justin Land, public affairs manager for Dow Chemical Co., the presenting sponsor.

The idea of combining education, entertainment, and economic development is so appealing that dozens of science festivals have cropped up nationwide since Philadelphia's first in 2011, according to the Science Festival Alliance, created a year earlier. Philadelphia is a founding member of the alliance.

While Philadelphia's celebration may never rival New York's $5-million-a-year World Science Festival, it is growing steadily. Attendance hit 100,000 last year. The final-day carnival on the Ben Franklin Parkway attracted 30,000.

The festival also has become self-sustaining, officials said. The $500,000 budget, covered by a grant from the National Science Foundation the first year, is now funded by sponsors, mainly Dow.

That underwrites a boggling array of grand, engrossing, and goofy opportunities for scientific edification. You can use a digital microscope to photograph your hair follicles at the University City Science Center. Build a robot at NextFab Studio on Washington Avenue. Brew cider and mead at Yards Brewing Co. Make slime and fizzy rockets at Smith Memorial Playground's Mess Fest in Fairmount Park.

"We like to say, 'We have fun down to a science,' " said Frederic Bertley, the Franklin Institute's senior vice president of education.

And then, in case any doubt persisted, institute staff did another don't-try-this-at-home experiment, turning half-gallon soda bottles into little bombs (again, liquid nitrogen was the key ingredient) that went off in a trash can filled with green and white plastic balls.

"Oooh! Cool!" the kids yelled.

mmccullough@phillynews.com

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