The British Pharmacopia 1898 with Indian and Colonial Addendum 1900.
About 600 pages describing all of the drugs in use at the time, how they were prepared, etc. etc.
What it doesn't say is what they were used for, since the pharmacist is supposed to prepare them, not prescribe them, but there's tons of interesting stuff, such as the way salicylic acid (aspirin) was prepared and how nasty it must have been in those days.
Ought to be pretty useful for Victorian/Edwardian RPGs etc. Unfortunately this is one of those books where it will be almost impossible to establish copyright status, with hundreds of contributors etc., so I don't think I can put it on line - and OCR would be a bastard due to the use of Latin etc. as well as English. Having said that, it may already be on line if someone has done the research, I haven't checked yet.
Meanwhile, if anyone needs any info let me know, I'll do my best to help.
Later - And before I started to look history_monk has found it on line!
And autopope has found an essential supplement covering more stuff, the extra pharmacopœia of Martindale and Westcott.
Also posted at https://ffutures.dreamwidth.org/2208464.html, where there are comments. Please comment here or there using OpenID.