108 METALLOSALINES. [IV. 



Compounds of Lead. — When metallic lead is calcined on tlie 

 hearth of a reverberatory, to which the air has free access, 

 it is converted into litharge, or simple oxide of lead ; and 

 when litharge is still further heated in a similar manner, it is 

 converted into a higher oxide, red-lead or minium, or orange- 

 mineral. Litharge, dissolved in vinegar, gives rise to acetate 

 or sugar of lead. White-lead is usually made by putting a 

 roll of sheet-lead into an earthen pot, containing a little 

 vinegar in the bottom, and placing a large number of such 

 pots in fermenting matter, manure, tan, &c. The fomenting 

 matter evolves heat, steam, and carbonic acid, and the heat 

 slowly evaporates the vinegar. This vapor induces the lead 

 to oxidize and form acetate of lead, which is decomposed by 

 carbonic acid as fast as formed, and the acid transferred to 

 the adjoining stratum of metal. In this manner the sheet 

 is corroded through, and becomes carbonate of lead, or white- 

 lead. Various other processes have been proposed, but the 

 old method still retains its place. 



White-lead. — Gannal gives a method of preparing it from 

 granulated lead by air and water. (Journ. Fr. Inst. 1847.) 

 See a review of the different methods in Journ. Fr. Inst. 1842, 

 vol. iii. 3d ser. p. 30. 



Disbrow Rodgers's process (Ch. Gaz. 1850) for the manu- 

 facture of carbonate of lead, consists in exposing thin sheet- 

 lead in a steam-heated chamber, to the joint action of acetic 

 and aqueous vapors, and of carbonic acid gas, generated from 

 fermenting matter contained in vessels beneath. The required 

 temperature is 80° F., and the vinegar is volatilized by the 

 admission of a current of steam. The chamber must be dark 

 and air-tight, and the fermenting and acid liquors renewed 

 six times during the process, at intervals of two days. The 

 conversion of the lead is completed in two weeks. See Review, 

 as above. 



White-lead Pigment. — According to Patterson (Ch. Gaz. 

 vii.), if a warm solution of chloride of lead is mixed with clean 

 lime-water, in such proportions that one equivalent of the 

 lead-salt may be made to react upon half an equivalent of 



