Fire Extinguisher on Wheels

On display outside of the Elizabethtown-Kitley Fire Station No. 3 in Frankville, north of Brockville, Ontario.

From what I've read, under a brass screw on the top would be found a glass bottle that held sulphuric acid.  When the extinguisher was tipped, the acid would pour into water and baking soda, creating carbon dioxide gas and tremendous pressure to expel the water.