=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. =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. [Illustration: View of Furnace for Making Sublimed White Lead] [Illustration: View of Goosenecks Used for Collecting Sublimed White Lead Fume] [Illustration: Bag Room Where Sublimed White Lead is Deposited _Photographs courtesy of Picher Lead Co._] [Illustration: Sublimed White Lead] [Illustration: View of largest Zinc Oxide Works in America, at Hazards, Pa.] =Sublimed Blue Lead.= Sublimed blue lead is made by burning coarsely broken lumps of galena, admixed with bituminous coal, in a special form of furnace. The fumes which are volatilized from this mixture are very complex in their chemical make-up, and in color are white, blue, and black. After being drawn through the cooling pipes by the suction of huge fans, whereby the fumes are cooled, the pigment is deposited in bags. This pigment is bluish black in color, and has been highly recommended for use on iron and steel. Its composition runs approximately as follows: Lead sulphate 50% Lead oxide 35% Lead sulphide 5% Lead sulphite 5% Zinc oxide 2% Carbon 3% [Illustration: View of Zinc Oxide Furnaces] [Illustration: _Photographs courtesy Geo. B. Heckel and N. J. Zinc Co._