It sounds like a drano bomb: http://www.snopes.com/crime/warnings/bottlebomb.asp
This guy here makes a very good argument that it is a reaction and not an explosion under ATF guidelines defining how strong something has to be to be an explosion:
http://answers.yahoo.com/question/index?qid=20110928103240AA...
He also notes that 2Al + 3H2SO4 -> 3H2 + Al2(SO4)3 is not on the prohibited list of reactions that are federally impermissible without a license.