I agree with rolla. If we are correct, it is intended to be connected to a tube rising from what is probably the oil filler of a machine with an oil sump. The oil in many such machines gets aerated. A vent directly on the original oil filler would be surrounded by a haze of oil mist when the machine was operating. This device would trap most of the oil vapour, and the little air filter on top would stop the remainder. Note that such a device could not legally have been used on a motor vehicle since about the 1970s, since it would defeat the positive crankcase ventilation system. It might have been intended for use on some kind of racing car, or an illegal street hotrod perhaps. Alternatively it might have been used on an industrial reciprocating air compressor, or a very old stationary engine that did not have PCV, to keep the machine and its surroundings from getting oily.
