The ammoia solution also had hydorgen mixed in with it. The heating
seperats out these two chemicals.When they recombine.they create an
endothermic reaction. Like those cold packs a sports trainer may use , on
the side lines.

The twop chemicals need to be mixed in a certin ratio. If one is in short
supply, the reaction stops.

I think it is the hydrogen leaking out, since it is so light and I can
hear liquid ammonia sloshing around inside wehn I burp one.