I have recently been given a number of double perforated 16mm family films,all taken in 1932 and 1933.
Inside one of the tins was the following piece of paper and I have included a pic of the base of the can showing the section you get wet.
Interesting,not sure if I wish to try this out.

The pad contained within the bottom piece of perforated metal had previously, before sale, been treated with a humidifier solution. This became activated when a small amount of water was added. Replacement pads could be purchased in packs.

The solution could be made at home and required the following:-
Distilled water
Glycerol
Camphor
Ethyl alcohol
Oils of eucalyptus, wintergreen, thyme, baptisia, mint.
The instructions said that a few drops on the pad in a 400ft humidor can was adequate. The film to be stored in a cool place.

Taken from the 1960 issue of The British Journal Photographic Almanac

Thanks Maurice, I had not seen the piece of card before and thought it a bit different.I liked the line “may take on a musty smell”,but to be fair if the original owner of the film followed the instructions then they worked well on the film in the cans as I am having fun watching films about hunting with dogs,Royal Marines training for the Royal Tournament and steam trains in 1932.

That just sounds like what someone should NOT be doing. Almost like an archivist nightmare.