1. _Litharge_ (PbO). This oxide forms when lead is oxidized at a rather low temperature, and is obtained as a by-product in silver refining. It is a pale yellow powder, and has a number of commercial uses. It is easily soluble in nitric acid: PbO + 2HNO_{3} = Pb(NO_{3})_{2} + H_{2}O. 2. _Red lead, or minium_ (Pb_{3}O_{4}). Minium is prepared by heating lead (or litharge) to a high temperature in the air. It is a heavy powder of a beautiful red color, and is much used as a pigment. 3. _Lead peroxide_ (PbO_{2}). This is left as a residue when minium is heated with nitric acid: Pb_{3}O_{4} + 4HNO_{3} = 2Pb(NO_{3})_{2} + PbO_{2} + 2H_{2}O. It is a brown powder which easily gives up a part of its oxygen and, like manganese dioxide and barium dioxide, is a good oxidizing agent. ~Soluble salts of lead.~ The soluble salts of lead can be made by dissolving (Pb(C_{2}H_{3}O_{2})_{2}.3H_{2}O), litharge in acids. Lead acetate called sugar of lead, and lead nitrate (Pb(NO_{3})_{2}) are the most familiar examples. They are while crystalline solids and are poisonous in character. ~Insoluble salts of lead; lead carbonate.~ While the normal carbonate of lead (PbCO_{3}) is found to some extent, in nature and can be prepared in the laboratory, basic carbonates of varying composition are much more easy to obtain. One of the simplest of these has the composition 2PbCO_{3}.Pb(OH)_{2}. A mixture of such carbonates is called white lead. This is prepared on a large scale as a paint pigment and as a body for paints which are to be colored with other substances. ~White lead.~ White lead is an amorphous white substance which, when mixed with oil, has great covering power, that is, it spreads out in an even waxy film, free from streaks and lumps, and covers the entire surface upon which it is spread. Its disadvantage as a pigment lies in the fact that it gradually blackens when exposed to sulphur compounds, which are often present in the air, forming black lead sulphide (PbS).