This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Boil 45 lb. asphaltum for 6 hours over a slow fire. During the same time boil 6 gal. oil which has been previously boiled, introducing litharge gradually until stringy, then pour the oil into the boiling asphaltum. Boil the mixture until it can be rolled into hard pills, let it cool, and then mix with 25 gal. turpentine, or as much as will give it proper consistency.