The Imperial Alchemist is named Shinjo-rushi. His apprentice, Tai Fong, was encountered during the Night of Gates. He was seen in a vision in the world above speaking with a skinwalking demon named Aku, who he seems to indicate has usurped the Dragon's place in the Cycle.
He is a different person than:
- The Ancient, who probably made the Terrible Oil of Wasting Death for Machan Li.
- Master Hsi, who made the Tincture of Pure Respite for the party
- Master Hsi's apprentices, who probably made the Tincture of Pure Respite for Machan Li
Takanata did some research on Alchemy in the Exalted Library:
> 1) What is the difference between Alchemy and Sorcery?
In general, Alchemy is the sub-specialty of sorcery which involves creating items by means of magic rituals. It seems to be one of the five-elements subspecialties which lets you use all of the elements, and there's a lot of overlap with "ritualist".
> 2) Are Alchemical Symbols more like a language that one learns, or a secret code that each alchemist invents for themself?
They're more like a convention, possibly backed up with a shtick. One alchemist might have a set of brushes of each animal hair - fox hair, bear bristle, magpie feather - for various symbolism, and another might use symbols. Alchemical symbols are also good for shaping the effect in a tidier way; you could have part of your ritual include inscribing a haiku about rain, or stamping the alchemical symbol for rain....
> 3) Are there any concepts that are naturally opposed to alchemy, the way cops are opposed to thieves?
.... not really. Something like Imit (destroying items to absorb the power) might be opposed to alchemy, or you could make the argument that natural philosophers are the natural enemy of sorcerers and all their ilk. [But sorcerers are related enough to be able to defeat/master fight an Alchemist.]
> 4) Is Alchemy related to demon summoning, or are those two separate arts?
Those are separate, though there is some overlap in the bind-a-spirit/demon-into-an-item domain.