Lead and Iodine form one combination, the protoiodide of lead (PbI). It falls as a bright yellow powder on mixing solutions of iodide of potassium and acetate of lead. It is slightly soluble in cold water, but much more so in hot water, from which solution it separates out on cooling in brilliant yellow silky scales.
Several oryiodides of lead also exist.
Lead and Bromine form protobromide of lead (PbBr), a white precipi tate resulting from the mixture of solutions of an alkaline bromide and a lead salt. From solution in hot water it separates out in white shining needles.
Lead and Chlorine form Protochloride of lead (PbC1), chloride of lead. It is best prepared by precipitating nitrate of lead with chloride of sodium ; it always, however, falls as a white powder when hydrochloric acid or a soluble chloride is added to an aqueous solution of a lead salt. Chloride of lead is soluble in boiling water to the extent of 3 per cent., depositing again on cooling in beautiful white silky needles. On the application of heat to it in the dry state it readily fuses, and solidifies on cooling to a semi-transparent mass termed horn-lead.
The orychlorides of lead are numerous. One occurs native (PbC1,2Pb0) [LEAD, Berzelite, in NAT. HIST. Div.] at the Mendip Hills, in Somerset shire, and is hence frequently called Afendipite. Another, the subject of a patent, and used as a substitute for white lead, is made by acting upon galena with hydrochloric acid, dissolving the chloride of lead thus produced in hot water, and precipitating with sufficient lime water to remove one half only of the chlorine. The re-action is as follows :— ,2Pbel + CaO = CaCI + no, net Chloride of lead. Llme. Chloride of calcium. Pattinson'aoxychloride.
Cassel or Turner's yellow is an oxychloride of lead, much used as a pigment. It is prepared by heating chloride of ammonium with ten times its weight of litharge.
lquorine and Lead form a white sparingly soluble fluoride of lead (PbF1).
Sails of Protoxide of Lead.
Carbonate of Lead This compound is precipitated as a white powder whenever solutions of an alkaline carbonate and a lead salt are mixed together. It is insoluble in water, but easily soluble in nitric or hydrochloric acids.
117ite-lead,as it occurs in commerce, is generally basic carbonate of lead, containing aboutP7 per cent. of linseed oil. It is also met with un
mixed with oil, and is then in the form of a heavy, white, amorphous powder, technically termed dry white-lead. White-lead may, however, as already indicated, be an oxychloride of lead, or even a neutral car bonate, and is often adulterated with sulphate of baryta, sulphate of lime, and carbonate of lime.
The old Dutch method of manufacturing white-lead consisted in sus pending thin sheets of lead in long wooden boxes, at the bottom of which was weak acetic acid. See LEAD MANUFACTURE . The boxes were placed in a close stove-room, were either surrounded with horse dung or had wine-lees put into them, and were subjected to a tempera ture of 85° to 90° for about a fortnight.
The changes which take place in this process may be shortly stated as follows. The spent tan, or horse-dung, or wine-lees, slowly decom pose, generating heat, and evolving carbonic acid. The heat volatilises the acetic acid, and this, with the oxygen of the atmosphere, forms with the metal a basic acetate of the oxide of lead. The carbonic acid derived from the eremacausis of the organic matter decomposes this basic acetate, forming carbonate of lead and neutral acetate ; the Latter soon becomes basic again, and the same decomposition goes on over and over again, till the metal is entirely converted into basic carbonate.
Phosphates of lead.—The alkaline triphospates, biphosphates, and monophosphates, give white precipitates with aqueous solution of acetate or other lead salt. They are all soluble in nitric acid, and have a composition corresponding to the alkaline phosphate that precipitated them. A chlorophosphate of lead PbC1) is found native. [LEAD, pyromorphite, in NAT. HIST. Div.] Sulphate of lead also occurs native. [LEAD, anylcsite, in NAT. DIST. DIP.] It is formed as a white precipitate on adding sul phuric acid or a sulphate to a lead salt. It is a heavy powder, soluble to a greater or less extent in ammoniacal salts and in hyposulphite of soda. It is also slightly soluble in strong nitrio or sulphuric acids : commercial sulphuric acid generally contains sulphate of lead as an impurity from the chambers in which it is prepared ; dilution with water precipitates it.