Swelling Solution is a potion that causes enlargement on contact. The user needs to brew this solution to cause a diversion in Chapter 11, Moment 1 of the Chamber Of Secrets on Pottermore, so you can collect a bicorn horn and boomslang skin from Snape's office.
From the Story
"Second-year Hogwarts students brew Swelling Solution in Potions class. This potion causes things to grow and expand. Its effects can be reversed with a Deflating Draught."
Making the potion
- Add 2 scoops of dried nettles to the mortar
- Add 3 pufferfish eyes to the mortar
- Crush to a medium fine powder
- Add 2 measures of crushed mixture to your cauldron
- Heat on a medium temperature for 20 seconds
- Wave your wand
- Leave to brew and return in 2-3 hours.
- Add 1 bat spleen to your cauldron
- Stir 4 times, anti-clockwise
- Heat to low for 30 seconds
- Wave your wand to complete the potion.