It's a drug that's made from a flower that's grown in India. It draws color from everything it touches. Years ago they tried it for bleaching cloth. They gave it up because it destroyed the material.
12 seconds sound clip from the The Invisible Man (1933) movie soundboard.
You can hear this line at 00:22:05.124 in the Blu-ray version of the movie.
Quote context
[...]
- You say he brought a packing case up here?
- The night before he disappeared, I heard him hammering, packing everything up.
- It's only a rough note, a list of chemicals. And the last on the list is monocaine.
- Monocaine? What is monocaine?
- Monocaine's a terrible drug.
- You wouldn't. It's never used now. I didn't know it was even made.
- That doesn't sound terrible.
- Yes, I know. But it does something else.
- Yes, and it also sent it raving mad.
- I only pray to God that Griffin hasn't been meddling with this ghastly stuff.
- He'd never touch a thing with madness in it.
[...]