This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A handy stamp moistener and envelope sealer can be made by procuring a small medicine bottle or glass vial and inserting a piece of felt or other wicking material in the place of the stopper, and filling it with water.
This moistener will be found handy for a small office where the mail is quite heavy, but not big enough to warrant the purchasing of a sealing machine. This moistener is sanitary and replaces the wet sponge. - Contributed by Theo. J. Becker, Kansas City, Mo.