(Breazeale and Benson, 1913)

The steam-pressure canner… is constructed of strong material and provided with a tightly fitting lid, which clamped in place makes it possible to hold steam under pressure and obtain a correspondingly high temperature….Most steam-pressure outfits will carry up to 30 pounds pressure with a corresponding range in temperature from 212° to 274°. Each steam-pressure outfit is equipped with a pressure gauge, which registers the pressure in pounds and the corresponding temperature: with a safety valve, steam petcock, and lifting crate.

--United States Department of Agriculture. (1921). Home canning of fruits and vegetables. Farmers' Bulletin, 1211. Retrieved from https://archive.org/details/CAT87202920

(Beveridge, 1953)

Pressure canners and cookers are made of materials strong enough to withstand pressure. Aluminum, either cast or heavy-gauge sheet, is most common. In hard-water areas the inside of an aluminum canner will darken but this does not impair its usefulness. Stainless steel is sometimes used for cookers and for canner lids, a special type of enameled steel for canner kettles. In the past, especially in times of metal shortage, some canner kettles were made of enameledware or tinned steel, both of which should be handled with care to avoid damage; too much heat above the water line of such kettles may cause tin to melt, enamel to crack.

 

--Pressure canners: Use and care. (1953). Beveridge, Elizabeth. Home and Garden Bulletin Number 30.