. Elements of modern chemistry . ing a soluble lead salt by an, excess of an alkalinecarbonate. A hydrated, and sometimes basic, carbonate of lead is knownas ceruse or white lead. Its composition varies. PbCO^ + H^O and 2PbC0 + Pb(0H)2 These are much used in oil painting. White lead is pre-pared by several methods, the oldest of which is called theDutch process. It consists in exposing sheets of lead to anatmosphere charged with acetic ^^^-^s^;^^;;;:^^.^^..^^^^^^^^ vapor aud rich in carbonic acid gas. The leaden sheets are introduced into glazed earthen pots, A (), containing a
. Elements of modern chemistry . ing a soluble lead salt by an, excess of an alkalinecarbonate. A hydrated, and sometimes basic, carbonate of lead is knownas ceruse or white lead. Its composition varies. PbCO^ + H^O and 2PbC0 + Pb(0H)2 These are much used in oil painting. White lead is pre-pared by several methods, the oldest of which is called theDutch process. It consists in exposing sheets of lead to anatmosphere charged with acetic ^^^-^s^;^^;;;:^^.^^..^^^^^^^^ vapor aud rich in carbonic acid gas. The leaden sheets are introduced into glazed earthen pots, A (), containing a small quantity ofvinegar. The lead rests upon shortprojecting arms, B, below which isplaced the crude vinegar. Thepots are covered by a disk of lead,D, which incompletely closes are then arranged in rows inlarge chambers; a row of pots isplaced on a bed of spent tan or horse-manure; these are cov-ered with planks, upon which more spent tan or horse-manureis placed, and then another layer of pots, and so on. The fer-. FiG. 110. LEAD CHROMATE. 343 mentation of the tan or manure raises the temperature to 30or 40°, and produces carbonic acid gas. On the other hand,the oxygen of the air intervenes, causing the lead to beattacked by the acetic acid, so that basic acetate of lead isformed upon the surface of the metal; but this salt is con-tinually decomposed by the carbonic acid gas, so that the leadgradually becomes covered with a layer of carbonate. Thenard suggested another process by which litharge is dis-solved in a solution of lead acetate, and a current of carbondioxide passed through the solution of subacetate so carbonate is precipitated and neutral acetate regenerated ;the latter is then again transformed into basic acetate. Theproduct so obtained is known as Clicliy white lead. LEAD CHROMATE. PbCrO^ This salt exists crystallized in nature, constituting the redlead of Siberia. It is prepared by double decompositionbetween solutions of potassium chrom
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