Alchemists' Guild or Workshop - Requirements?

Hi everyone, am playing the Grand Camapign as the Turks and have just reached the age of gunpowder...

One of the new building options available to me is the Alchemists' Workshop which is NOT a guild but a normal building I can build. It costs about 1200 florins and allows gunpowder weapons to be upgraded.

But... I can only build it in Jerusalem. Only reason I can find is that I have the Explorer's Guld HQ there. No other settlement has the HQ and no other city can build the Workshop.

Anyone know why this is so?

There are three tiers of the Alchemist lab.
Tier 1 alchemist lab: (needs a great market) upgrades mêlée weapon gunpowder units (+1).
Tier 2 alchemy school: (needs a merchants quarter) upgrades mêlée weapon gunpowder units and artillery units (each +1).
Tier 3 university: upgrades weapon_projectile 1 (musket / arquebus etc. +1?) I have no idea what this upgrade really means. The swordsmith gives an upgrade of +1 to weapon which is according to test +6. Is this the same with the musket and other gunpowder weapons?