Chemistry blocks (the ones that are implemented, that is) are already present OOB with PocketMine-MP unconditionally. Unfortunately, they don't render correctly due to weirdness in the way Mojang handles the resources.
- Download the
manifest.json
file from this gist. - Add it to a zip file (on Windows, right click -> Send to -> Compressed (zipped) folder)
- Place the zip file in PocketMine-MP's resource pack folder and enable it like a normal resource pack.
- Profit!