This comes under Polishing. "When a film is finished it should be polished to remove finger marks, dust, etc, from the back. For this purpose a small felt pad is obtained and placed in the centre of the re-wind table. It should be just saturated with it, but not to the extent of allowing the alcohol to drip out of the pad. The film is now wound from one spool to another, and as it is passed over the pad, the back is rubbed with alcohol. This has the double effect of cleaning the emulsion side of the film with the felt and cleaning the back with alcohol".
"The film should be stored in a humidor tin. This is a tin large enough to contain the film and spool, at the bottom of which is a pad containing suitable chemicals, which is moistened with water. This keeps the film moist and prevents it from becoming brittle. This is the only satisfactory way of preserving film, and if films are kept in any ordinary atmosphere for any length of time, they will soon be found to be continually breaking. This is the formula for the preservative:

Distilled water ......7ozs
Glycerol .......1 and half ozs
Ethyl alcohol .....2ozs
Camphor ..........1oz
Menthol .......half oz
Oil of Eucalyptus ........1oz
Wintergreen, Oil of Thyme, Oil of Baptisa, and Oil of Mint.......half an ounce each.

Add the Glycerol to the distilled water and mix thoroughly. Dissolve the Camphor and Menthol in the alcohol. Mix the oils together and add to the alcohol, finally pouring this mixture into the water and glycerol. Shake well before using. Use a teaspoonful for each 400ft film.

Robert,
Just so I am understanding correctly, is this how we should preserve our films now, or is this how it was once done (hence the title 'Film Preservation 1930s style')?

This is how it was recommended in a book published in 1933, this formula was still appearing in print elsewhere in the early 60s.

Was it recommended both for acetate and nitrate films?

This was for amateurs, so would be safety film. I think you could have problems getting one or more of the ingredients now. There was a time when you could get anything made up by a Dispensing Chemist, now they print labels and stick them on a box taken off a shelf. No skill there.

I would think this solution would be quite safe with modern film stocks, although beware plastic spools, it might weaken them.