It's easy, really, if you're clever. A few chemicals mixed together, that's all. And flesh and blood and bone just fade away.
10 seconds sound clip from the The Invisible Man (1933) movie soundboard.
You can hear this line at 00:18:28.575 in the Blu-ray version of the movie.
Quote context
[...]
(THE INVISIBLE MAN LAUGHING MANIACALLY) (3)
- How can I handcuff a bloomin' shirt?
- Are you satisfied now, you fools?
- A little of this injected under the skin of the arm every day for a month.
- Not if he can't get no further than this room, he won't. Here, shut that door.
- Now, then, you'd better come along quietly.
[...]