Sheet iron box luted at bottom with water. Atomized lead, blown into box with steam, falls to bottom and becomes hydrated (Mild Process)
Photographs courtesy of Stowe Neal
View of agitation tanks for making Mild Process Lead
White Lead (Mild Process). The Mild Process of manufacturing white lead consists of first [melting the pig lead] and converting it into the finest kind of lead powder, then mixing thoroughly with [air and water]. The lead takes up water and oxygen and forms a basic hydroxide of lead. Carbon dioxide gas is next pumped slowly through the [cylinders] which contain the basic hydroxide of lead. The result is basic carbonate of lead—the dry white lead of commerce. The process is called “Mild” because it is the mildest process possible for the manufacture of white lead. It is the only method in practical operation which does not require the use of acids, alkalis or other chemicals, every trace of which should be removed from the finished product by expensive purifying processes. The failure of such washing and purifying means a product of inferior quality, which necessarily reduces the durability of any paint in which it is used.
Steam Jected Pans for Drying White Lead
Basic Sulphate-White Lead (Sublimed White Lead). By the action of the oxygen of the air on the fume produced by the [roasting] and subsequent volatilization of galena, this fine, white, amorphous pigment is made. On analysis, its composition shows approximately 75% of lead sulphate, 20% of lead oxide, and 5% of zinc oxide. It has a specific gravity of 6.2. Possessed of extreme stability, it finds wide use as a constituent of paints and as a base for tinting colors. The [photomicrograph] of this pigment shows its extremely fine, amorphous nature with complete absence of crystals. In fineness it closely approaches zinc oxide. On account of its non-poisonous properties it is replacing corroded lead in many places. Unified paints containing sublimed white lead are of great value, showing upon long exposure very little decay.