Main Walkthrough

Prerequisites: Complete Unknown Residue and Annoying Bugs (unverified)
Reward: Cerulean Scrub, Peppers Ointment, Popping Aid, Alacrity Concoction, and Swirl Solution Recipes

Unlocks: --

Head back home after finishing up Unknown Residue and Annoying Bugs. (I'm not 100% positive that you need to complete both of those quests, though given that they both get in your way when you approach unexplored territory it's almost certain that one of them keeps this one locked.) After snoozing you'll be greeted by Xiao and Collin, and Collin will declare that you're up for promotion. Time for The First Chemistry Test.

Head to the Research Bench and fill the spyglass with Wind and Water icons. This will finish up the research and give you your next Potion: Blue Blood, a typical test concoction for up-and-coming chemists. The Blue Blood crafting template has fifteen spaces to fill, and you can only use Water and Wind materials so your options are, for the first time, limited. Here are some suggestions for getting the job done:
  • The top-most line of three blocks is most easily filled by Konjac. Konjac was unlocked by completing Annoying Bugs, and the chances that you have one are pretty high. 
  • The remaining twelve slots can be filled in by three Rainbow Dews. Rainbow Dew was allowed to grow again thanks to your completion of Unknown Residue, and is found in the south of Meadow Range.
  • Alternately, if you'd rather not use up all of your Rainbow Dew, you can use one Lavender, one Sour-Tasting Sap, one Sticky Jelly, and just one Rainbow Dew to fill in the remaining spaces. Lavender is found throughout the Heart of Meadow Range, Sour-Tasting Sap comes out of the red trees in the same area, and Sticky Jelly is pulled from dead Green Blobs.

Take the resulting Blue Blood to Xiao, likely over at Town Hall. You'll get shuttled to the ground floor of Town Hall to meet with some familiar Medical Association members, and they'll give you a bundle of Potion Recipes as a reward: Cerulean Scrub, Peppers Ointment, Popping Aid, Alacrity Concoction, and Swirl Solution. With these you can now cure more advanced illnesses.

Head to bed once you're done with your day. The next morning Collin will show up at your door, and he will give you a Letter of Recommendation. You can give this to Mayor Myer to complete another quest, First Badge Promotion.