You were experimenting with three elements, as I remember: exnide, ethna bromide, and something else.
9 seconds sound clip from the Monsieur Verdoux movie soundboard.
You can hear this line at 00:54:47 in the Blu-ray version of the movie.
Quote context
[...]
- Chemistry, my dear fellow, is the material manifestation of the metaphysical.
- Do you remember some time ago discussing a humane method of doing away with dumb animals?
- A lethal formula for veterinary work? No pain. No convulsions. Absolutely tasteless.
- The creature drinks it and in about an hour curls up into a comfortable sleep and dies.
- Yes. That was very interesting, pharmaceutically.
- The results are interesting.
[...]