Almost certainly a chlorate or perchlorate (sodium or potassium salt). Think swimming pool chemicals, particularly like a "shock" treatment chemical. It's undoubtably a powerful oxidizer and the instructions for grinding it on an organic substrate (wood) plus the claim that one may "purify" (disinfect, actually) drinking water with it points VERY strongly at the common swimming pool treatment chemicals. Don't try this at home with a big pile of the stuff from the pool supply section of your local store unless you already know what to expect. Any further discussion will probably bring the HLS folks sniffing after me, so I'll stop here.

I don't regard it as a useful inclusion in a prepared kit. Knowing how to do that sort of thing in a MacGuyverish situation is great, but otherwise it's an unreliable gimmick IMHO.

Tom