In the early 1950s I had a chemistry set which had a bottle of urea crystals. Upon finding out what it was, I left it alone in disgust until....a few years later we (that old gang of mine) began experimenting in making our own July 4 fireworks and skyrockets. It came in handy then. BTW, by the late 70s/early 80s, that compund was not to be found in chemistry sets: too dangerous; a kid might try to make his/her own fireworks!---John