I have a couple of these around although I have never used them and for good reason.
It consists of a small syphon type spray gun that can use either a glass color cup or special bottles of Dupli-Color paint. It is attached to a small aluminum diaphragm style compressor(or if you prefer it can be hooked to the valve of a spare tire) which is operated by removing a spark plug in the engine and screwing it in to the plug hole. The thread on the compressor is 14 mm but there are two adapters included for 10 mm and 18mm plugs. You simply start the engine and the piston movement operates the compressor. I assume that to get more pressure you merely rev up the engine.
What scares me about this rig is that on the bottom side of the compressor are vent holes to allow excess pressure to escape into the atmosphere.... along with vaporized gasoline! Imagine the vapors building up in the engine compartment and the loose spark plug wire suddenly grounding out on a piece of metal.At the very least the hood would be blown off the car.
The copyright date on the box is 1950 although the illustration shows a much earlier vehicle;suggesting these had been around for awhile. I have several other similar types that use the spare tire for an air source and they date to the 1930's, What were these people thinking?

I remember years ago using a sparkplug rig to inflate farm machinery tires. Had an old refrigerator compressor/motor for use around the shop.

What were they thinking?   Hard to say, but a lot of stuff was buy, and use at your own risk.   Back then before fan clutches, that big steel fan was moving all the time, pushing lots of air around to dilute the vapors.   Plus the hood would probably be open.  I could blow but one would probably work at it.  Got one of those old spark plug tire inflators.   Old farmer used it often on tractors parked a long way from the shop. 

My first thought  was that I could use it to spray some solvent, or other flammable, to degrease something in the engine compartment. Maybe for cleaning up the battery?



Chilly

In Australia these were very common to the late 80's they were called a Menzel pump and were always included as outback recovery gear, then Cars started having no spark plugs and or diesels so people had a fitting welded to the exhaust manifold.......nowdays of coarse everyone has a 12 volt compressor....they were only used here from pumping up tyres ......could you really imagine spray painting with exhaust and petrol exhaust gases, the carbon and oil ect would surly make a mess of paint you would need one hell of a good filter

I still have a spark plug inflator. It was mandatory eqpt when in the "back country".