In a world where magic exists, and high technology does not, we often forget the myriad uses of basic chemistry and metallurgy, throwing them away because they do not fit our idea of the pre-industrial society. Yet, they are valid fields of study for the idle rich, for the sage who wishes complete understanding, for the smith, and especially for the Alchemist. So, let's consider what things can be made from readily available materials.
Much of inorganic chemistry is centered around acid and base reactions. Sulfuric acid can be readily, even easily obtained by burning sulpher and saltpeter, both obtainable from nature with little refinement, in the presence of steam. Distill this liquid in the presence of table salt, and you have muriatic, or Hydrochloric, acid. More difficult to obtain is nitric acid, which can be made by greatly heating air, and combining the resulting gases with water. Once these three are found, a wide number of useful reactions can occur.
Notably, Nitric acid and its salts can be used to create a wide number of highly flammable, even explosive substances, of which one of the easiest is guncotton, made by soaking cotton in a mixture of nitric and sulfuric acids. Highly explosive and highly unstable, this material can be used for blasting and as cannon-powder.
Many metal salts can also be obtained by leeching ores in acids. Some of these salts may be reduced by heating with methane, aka, swamp gas. While metals created in this matter will be extremely expensive, the addition of even half a percent by weight of materials such as nickel or chromium can cause drastic changes in the properties of steel. Stainless steel may not be unknown to the nobility, and it is said that Napoleon fed his most favored guests off of aluminum plates, while the less important had to be content with gold!
If those of the researchy bent have access to a source of electricity, (Cue rod of lightning jammed sideways in a device), electrolysis may also exist. With electrolysis, what salts cannot be easily reduced to their metals can be purified, though the electrolysis bath can become very exotic very rapidly.
Well, all that is excellent trivia, but what good is it? After all, it's expensive, and not nearly as reliable or timely as an incantation - or is it? Such chemistry allows the enormously wealthy new materials of construction: Alloys that may be harder, stronger, and more durable than the common carbon steel. Armor may be feather light, untarnishing, or simply resistant to heat, or possibly even magic. You may not be able to give your soldiers all +1 weapons, but you can give them all stainless swords that hold an edge. Guncotton allows for fearsome traps on the field of battle, and demolitions work on untold of scales. Many things are available, but not economical - But this doesn't neccesarily exclude them from play in the hands of (creative) NPCs. The laser gun may as well be magic - But the man with the arquebus squad is something else entirely.