On this page of the guide to BioShock Infinite, you will find information about where to find infusions / essences in chapters 28-31 and chapter 35. Information about each infusion features a description and a picture. There are 6 infusions to find in chapters 28-31 and chapter 35.
Grand Central Station - inside a locked room to the left of the entrance to the station.
Salty Oyster Bar - in a locked room behind the bar (it requires Voxophone #56).
Market District - inside a bedroom on the first floor of Lutece Lab.
Market District - in a locked Wilson Bros. & Company liquor store.
Financial District - inside a secret room at the end of the corridor to the left of the vault (Vox cipher is required).
The Operating Theatre - inside a closed office located above the operating room.