Hot Rods Anyone know what this is...

Killing time looking at classified ads and found this photo. I'm curious about the canister or tank on the passenger side of the firewall. I'm guessing it's something connected with the lubrication system, filter maybe or extra capacity, anyone seen one before or know what it is?

 

Vacuum tank for the wipers? Just guessing...

 

It's an accessory overflow cannister

 

Yep, Chevy coolant overflow tank. Around 1937-1948.