Any alchemist worth his salt will tell you, quite indignantly, that his art is one of precision and knowledge... none of the mumbo-jumbo practised by wizards nor the reliance on quite unreliable deities of the cleric. Here that art is distilled out and its practice transformed into something actually actively playable, not just something your character does during downtime to give himself some exotic weapons and other useful items.
Once you get past the historical notes and the basics of the Alchemist class, there is an array of procedures that must be mastered and interesting plants to be gathered. There is also a list of items that the well-equipped Alchemist should have to hand - most of this is included in a standard 'Alchemist Laboratory' but if you drop a beaker, say, it's useful to know what a replacement would cost.
We then move on to alchemical operations. Naturally, what each Alchemist can do increases by level Ominously, this opens with a note on explosions - the accidental sort, not those created by design. These end with the advice to consider leaving town... Hopefully, your Alchemist will not need to flee, but will be kept busy making a range of elixirs, powders and other substances to create a wide variety of effects. Just make sure no contrary vine gets into the mixture, as this reverses the effects of the substance!
As the Alchemist's level increases so do his skills - quite dramatically! Care should be taken that his abilities do not outstrip those of other members of the party. Oh, and by tenth level there will be prospective apprentices banging on the door seeking to study with him.
This is followed by an extensive DM's Section. This looks at all aspects of moderating an Alchemist character from how to start him off to how to judge his own creations (as the sort of player who wants to run an Alchemist in the first place will probably tire of the admittedly massive lists already presented and start to invent his own). There are also notes on trading in alchemical substances - some may use their skills to raise funds, and of course anyone may wish to purchase items when the party Alchemist is too busy to make what they want.
To help maintain balance, there are suggestions about how to award an Alchemist experience, ensuring he gets fair recognition for lab time without making it excessive. This is a game about adventuring, after all, not working at the lab bench! There are also notes about portable labs, as when out adventuring, that poor Alchemist may be pining for his laboratory, or may run short of things he could make did he but have access to it.
Most Alchemists have studied under a master, and there's a quick route to generating that master should you not have one in mind. Likewise, they may need hirelings to assist in their work and, as mentioned above, will attract students of their own. Again there are notes to help you create all the folk you need... not, of course, always the model lab staff the Alchemist would like. Alchemists and Wizards can work together - when not engaged in debate on the relative merits of their studies - and notes on this is followed by some on possible ingredients from monsters and other sources.
This is a masterful exposition of how to run alchemy in the context of a fantasy game and ought to be read by anyone with an interest in the subject irrespective of the ruleset they use. You can always tweak the rules to suit your chosen system: it's the ideas that are of real value!