You're likely thinking about Lithium Hydride or Calcium Hydride.

It was used a lot in WWII to inflate balloons for emergency
communications in life rafts.

I beleve that Fair Radio Sales still sold some of these canisters as of a
few years ago, try a web search.

However, the residue from these canisters is highly corrosive,
and hydrogen is VERY inflammable, and you'd likely need to 
engineer some type of water bath (a LOT of heat is generated)
amd tube to conduct the H2 to the balloon.

Are you sure you need to do this ?

Ham radio operators have come up with very invovative ways of
getting a signal out of the wilderness, with improvised and
light weight materials.

Give us a few more details, and perhaps we can help further.

Daryl 
 
__________________________________________________________

Public Seismic Network Mailing List (PSN-L)