"The Cat's In The Bag..."
Season 1, Episode 2

Walt and Jesse are now left with a half-dead Krazy-8, and a lifeless Emilio. So, what to do with a body laying around? 

Walt needs to leave no evidence behind, so Walt uses his chemistry knowledge to think of a scientific way to dispose of this bag of flesh: by putting it in hydrofluric acid. By placing Emilio's body in the acid, it'll turn into an unidentifiable slush. Unfortunately, Walt leaves out the very important detail that, though it won't eat through plastic, hydrofluric acid will eat through rock, steel, glass and ceramic. By the time Walt realizes that Jesse had mistakenly put the acid in the bathtub, it's too late, and the slime falls through the floor.

But, the plan worked; and hydrofluric acid was used many times from there on out. It changed the game and made murder a crime that could be done without consequences or evidence.