As this is an old photo and the unit is powered you may well find its a tricoethylene vapour cleaner/ Ultrasonic cleaner, I use to run one big enought to submerg a complete car engine until the law forbid the use of tricoethylene 111.
It would gently heat the item and clean it at the same time, also very useful when replacing valve guides into Engine blocks as the heat was gentle without causing hot spots and distortion, a few of my mates use to put there home made wine into the unit claiming it aged the wine, I never tasted it to see.
Oh for the good old days.