I have four of what appears to be the same thing. They are soda-acid extinguishers. The water has baking soda mixed in with it. The glass bottle is about 1/4 to 1/3 full of sulfuric acid. There is a loose lead plug in the top of the bottle called a stopple. Its purpose is to prevent the water from mixing with the acid inadvertently when the extinguisher is being carried around. As was said before, to use the extinguisher you just turn it upside down. The stopple falls out and the acid mixes with the base (baking soda or sodium bicarb). The reaction creates CO2, discharging the water under pressure. The soda tends to settle into the bottom over time, reducing the effectiveness of the stream. There have been reports of very old ones exploding if someone tries to use them. The safest thing to do is to carefully remove the bottle of acid, cap it and properly dispose of it. I've tried to sell mine (my dad bought them for a house that we had moved into in 1954), but no takers so far.
Stay safe out there, everyone goes home!