Perhaps you should read the basics about this site. Alchemy roughly has 4 disparate goals: transmutation of base elements into noble elements, elixir of immortality, healing medicines, and creation of a "universal solvent". The only thing that is remotely scientifically possible is medicines, but you're not asking about that. Since black powder was in use in the 11th Century (China) and had improved enough by the 13th Century to allow bombs and explosives, I don't understand what you are asking. Various fluids were also used in flame-throwers and in bombs as incendiaries. White phosphorus was discovered in 1611 and is a very nasty (and commonly used) chemical weapon - it ignites about 30°C (86°F) so it doesn't take much heat to ignite it. It is a weapon of fear; since it continues to burn on contact with skin or water, no one with any sense wants to be anywhere near it. Napalm, or gelled gasoline (or mineral spirits), would be another easy weapon to make, with all the ingredients known at the time. Greek Fire dates to ~ 670 C.E. but of course weapons using fire are known as far back as the 8th Century B.C.E. Also, there's no real reason why biological weapons couldn't be used. Weaponizing some of the germs isn't very hard, at all. But for obvious reasons, I'll not describe the process here. (Hint: you grow the germs, and you put them onto dust which will blow in the wind.) Of course none of these are particularly appropriate for person-to-person weapons. Its useful to know that up until the 20th Century, more soldiers (and civilians) died during wars of disease than from enemy weapons. If you've got steam, then it seems to me that weapons using steam instead of black powder are possible (using a large boiler), so that rapid fire guns should be possible, "rapid" in the sense that rather than having to reload the tube with powder, wad, and shot, you could just put the wad & shot in without having to cool down (swab) the barrel.

Perhaps you should read the basics about this site. Alchemy roughly has 4 disparate goals:

• transmutation of base elements into noble elements
• elixir of immortality
• healing medicines
• creation of a "universal solvent"

The only thing that is remotely scientifically possible is medicines, but you're not asking about that. Since black powder was in use in the 11^th Century (China) and had improved enough by the 13^th Century to allow bombs and explosives, I don't understand what you are asking. 

Various fluids were also used in flame-throwers and in bombs as incendiaries. White phosphorus was discovered in 1611 and is a very nasty (and commonly used) chemical weapon - it ignites at about 30°C (86°F) so it doesn't take much heat to ignite it. It is a weapon of fear; since it continues to burn on contact with skin or water, no one with any sense wants to be anywhere near it. 

Napalm, or gelled gasoline (or mineral spirits), would be another easy weapon to make, with all the ingredients known at the time. Greek Fire dates to ~ 670 C.E. but of course weapons using fire are known as far back as the 8^th Century B.C.E. 

Also, there's no real reason why biological weapons couldn't be used. Weaponizing some of the germs isn't very hard, at all. But for obvious reasons, I'll not describe the process here. (Hint: you grow the germs and you put them onto dust, which will blow in the wind.) Of course none of these are particularly appropriate for person-to-person weapons.

It's useful to know that up until the 20^th Century, more soldiers (and civilians) died during wars of disease than from enemy weapons. If you've got steam, then it seems to me that weapons using steam instead of black powder are possible (using a large boiler), so that rapid fire guns should be possible, "rapid" in the sense that rather than having to reload the tube with powder, wad, and shot, you could just put the wad & shot in without having to cool down (swab) the barrel.