2 PbCO₃.Pb(OH)₂, containing 86·27 per cent. of PbO. 5 PbCO₃.2Pb(OH)₂ ” 85·86 ” ” 3 PbCO₃.Pb(OH)₂ ” 85·45 ” ” 4 PbCO₃.Pb(OH)₂ ” 85·00 ” ” According to Hochstetter, the manufacture of white lead must be directed to obtaining the compound 2 PbCO₃.(OH)₂, which possesses the following percentage composition:— PbO 86·32 CO₂ 11·36 H₂O 2·32 The compound of this composition is distinguished by being completely amorphous, and so possesses the greatest covering power. Commercial white leads, as is seen from the formulæ of Mulder, may differ appreciably from this composition, when they will have a smaller covering power, since they will contain some quantity of neutral lead carbonate, PbCO₃ (containing 83·46 per cent. of PbO), which is crystalline. White lead is prepared according to very different methods, the principle of which consists in subjecting a solution of tribasic lead acetate to the action of carbonic acid, by which the basic carbonate is produced and the neutral acetate formed, the latter being then reconverted into the basic acetate, which again serves to produce white lead and so on. CHAPTER VII. THE MANUFACTURE OF WHITE LEAD. The processes by which white lead is or was manufactured may be divided, according to the principal operations, in the following manner:— 1. Processes in which metallic lead is subjected to the action of acetic acid vapour, whilst the vessel in which this operation is conducted is exposed to a higher temperature. In the oldest so-called Dutch method this increase of temperature is effected by the decomposition of manure, by which the vessels containing the lead and acetic acid are surrounded. In consequence of the heat produced by this fermentation, acetic acid and water are volatilised, and oxygen also being present, lead acetate is formed. Also, as a consequence of the oxidation of the lead, heat is produced, which accelerates the process, and lead oxide is formed in large quantity, which unites with the neutral acetate already formed to produce a basic compound. The vessels in which this process is taking place are in an atmosphere containing much carbonic acid produced by the fermentation of the surrounding organic matter; this carbonic acid converts the basic lead acetate into white lead. The German or Austrian method is to be regarded as an improvement on this rough process. The heat necessary for the normal course of the chemical reactions is produced from fuel; the carbonic acid formed by the combustion of the fuel is used to convert the basic lead acetate into white lead.