Pesky Sulfur

[DizzyZ1991]

So, I have played through the entire game until the Examination Room. I went in once before to have a look around and picked up the Acetone and Nitrogen, and moved some books around. Later, when the game took me back to that room, I gathered all the other chemicals and put them in the machine -- except for Sulfur! I can't seem to find it anywhere! I've looked behind all of the books on every desk and shelf, and I've also searched the floor. I tried reloading the room, and it's still not there. Please help?