In the army we had grenades with white phosphorus that would burn under water. Also napalm is very hard to put out. And thermite can be produced in a fairly simple fashion, but it needs magnesium to light it.

i used a pitch/ saltpeter/ grape vine charcoal mix. I havent got the weight down, i tend to just toss some in. 

Goodness gracious great balls of fire!

I am in a singing mood........

Smoke on the water.........FIRE IN THE SKY!

(with head banging)

Hey pretty neat recipe for poison gas that I found

Human excrement dried powderd and finely sifted            15 lb
wolfs bane                                    8oz
Aconite                                          8oz
Croton oil                                    8oz
Soap-bean pods (to make the smoke)                  8oz
Arsenious oxide                                    8oz
Arsenic sulfide                                    8oz
Cantharides beetles                              4oz
Ashes                                          16oz
Tung oil                                          8oz
Total                                          316oz

That was taken from the military encyclopedia by tseng Kungliang (A.D. 1044)

Just a few questions what the heck is: wolfs bane, Aconite, Croton oil, Arsenious oxide, Cantharides beetles, and Tung oil? Also I hear that greek fire had sulfur ,saltpeter, gasoline, (I assume its something different from the gas we use today but Im most likely wrong) pine resin, and gum resin.      In other recipes they  mention tow. I think its called tow anyway, but what is it and how was it made? Thanks.

Wolfs bane(wolfsbane) - aconitum napellus, one of most toxic herbs available
Aconite - aconitum, napellus or lycoctonum 
Croton oil - oil from croton tiglium, bright coloured plant often grown as a houseplant
Arsenious oxide - oxide of arsenic, probably As2O3, arsenic trioxide
Cantharides beetles - some beetles which have cantharidine(pretty potent poison) in them - that's almost every beetle which lives underground, check your favourite "poisonous insect guide"
Tung oil was already explained.
Tow is the strange thing which is produced in the process of flax dressing. It is widely used by plumbers to seal threads and such - wrap with a tow, apply some oil or vaseline and screw it tightly. Any plumber's shop will have it.
Wolfsbane is so called because aconitum roots were placed in pieces of meat and scattered across the land, wolves ate it and the roots kill them.
If you just want to generate  posion gas, use dried, powdered aconitum roots OR(not and) arsenic trioxide as a additive to a sugar/saltpeter mixture(or blackpowder/oil, if you want to be medieval - this mixture was used with an aconitine to poison people in castles and such, setting everything on fire meanwhile) and sod beetles, excrements and such. It is not important and, in the case of beetles, hard to find in enough quantity.

Hope that helps.

haha yes that helps. i was not wondering where i could get it or what i could use as a replacement, explosions and fire are my thing not poison gas. But thanks for all the info anyway!

by the way where could you get sulfer naturaly? burning somethings will release it or make it but im not positve i rember what.

also i was wondering, today we get lead from tires and fishing weights, but how would they origanaly mine the stuff? was there a lead ore? if so what did it look like where could you find it?