What is this? (gm part)

[maxwedge528]

i was under the hood of a very original 55 cadillac sedan deville yesterday and it had a similar glass jar! windshield cleaner reservoir? as a matter of fact there was a gm label advising the owner to empty the bottle in the winter or to mix the water with GM something or another to prevent freezing. also surprising that the manual fuel pump was installed on the top of the motor kinda of in the area of the water neck to the top radiator hose.