A leavening agent is an organism or substance that when added to a dough[?] of flour and water causes it to "rise" by evolving carbon dioxide or other gasses that become trapped as bubbles[?] within the dough.
... Liverpool
Walker Art Gallery[?]
Northamptonshire
Earls Barton Museum of Village Life[?]
Northampton Central Museum & Art Gallery[?]
Norfolk
Bressingh ...