White of Lead ,

The two methods are in Jiudan jingjue, i7.3a-b. See also 20.15a, where the compound is called White of Lead qianbai). On the method of the Flowery Pond found in the original Scripture of Great Clarity see below in the present chapter. 

Salter, writing in 1869, states that the whites of lead are carbonates of that metal with two exceptions - Flemish white or the sulphate, and Pattison s white or the oxychloride . Field (1835) specifically remarks that Flemish white is an exceedingly white precipitate from any solution of lead by sulphuric acid much resembling the blanc d argent . Harley (1982) states that the chemist and author Bachhoffrier (1837), who also acted as an artists colourman at that time, is recorded as selling the precipitated lead sulfate imder the name Flemish white. Mayer (1991) on the other hand gives this term for lead white (q.v. ). 

The white precipitate of lead hydroxide (or hydrated lead(ll) oxide) is then oxidised by the chloraie(I) lo the brown dioxide ... 

If the normal carbonate is used, the basic carbonate or white lead, Pb(OH),. 2PbCO,. is precipitated. The basic carbonate was used extensively as a base in paints but is now less common, having been largely replaced by either titanium dioxide or zinc oxide. Paints made with white lead are not only poisonous but blacken in urban atmospheres due to the formation of lead sulphide and it is hardly surprising that their use is declining. 

Lead(II) in aqueous solution gives on addition of the appropriate anion (1) a white precipitate of lead(II) chloride, (2) a yellow precipitate of lead(II) chromate, and (3) a yellow precipitate of lead(II) iodide which dissolves on heating and reappears on cooling in the form of glistening spangles . 

When an element has more than one oxidation state the lower halides tend to be ionic whilst the higher ones are covalent—the anhydrous chlorides of lead are a good example, for whilst leadfll) chloride, PbCl2, is a white non-volatile solid, soluble in water without hydrolysis, leadflV) chloride, PbC, is a liquid at room temperature (p. 200) and is immediately hydrolysed. This change of bonding with oxidation state follows from the rules given on p.49... 

Prepare a solution of sodium plumbite by adding 10 per cent, sodium hydroxide solution to a few drops of about N lead acetate solution until the white precipitate of lead hydroxide initially formed just redissolves to a clear solution. Add 1 ml. of the fusion solution the presence of sulphiu- is indicated by a black precipitate of lead sulphide. 

The metal is very effective as a sound absorber, is used as a radiation shield around X-ray equipment and nuclear reactors, and is used to absorb vibration. White lead, the basic carbonate, sublimed white lead, chrome yellow, and other lead compounds are used extensively in paints, although in recent years the use of lead in paints has been drastically curtailed to eliminate or reduce health hazards. 

PbO PbO H2O, for example, may be formed by boiling suspensions of lead oxide and lead sulfate in water. In addition, complex mixed salts, such as white lead, 2PbC02 Pb(OH)2, are readily formed. 

Lead Chloride. Lead dichloride, PbCl2, forms white, orthorhombic needles some physical properties are given in Table 1. Lead chloride is slightly soluble in dilute hydrochloric acid and ammonia and insoluble in alcohol. It is prepared by the reaction of lead monoxide or basic lead carbonate with hydrochloric acid, or by treating a solution of lead acetate with hydrochloric acid and allowing the precipitate to settle. It easily forms basic chlorides, such as PbCl Pb(OH)2 [15887-88 ] which is known as Pattinson s lead white, an artist s pigment. 

Lead borate moaohydrate [14720-53-7] (lead metaborate), Pb(B02)2 H20, mol wt 310.82, d = 5.6g/cm (anhydrous) is a white crystalline powder. The metaborate loses water of crystallization at 160°C and melts at 500°C. It is iasoluble ia water and alkaHes, but readily soluble ia nitric and hot acetic acid. Lead metaborate may be produced by a fusion of boric acid with lead carbonate or litharge. It also may be formed as a precipitate when a concentrated solution of lead nitrate is mixed with an excess of borax. The oxides of lead and boron are miscible and form clear lead-borate glasses in the range of 21 to 73 mol % PbO. 

The most common white pigments are titanium dioxide, 2inc oxide, leaded 2inc oxide, 2inc sulfide [1314-98-3], and Hthopone, a mixture of 2inc sulfide and barium sulfate [7727-43-7]. The use of lead whites and antimony oxides has been decreasing steadily for environmental reasons. 

Lead Whites. Basic lead carbonate, sulfate, siHcosulfate, and dibasic lead phosphite are commonly referred to as lead whites. Usage is limited because of environmental restrictions placed on the use of lead-containing compounds. 

Properties. Thallium is grayish white, heavy, and soft. When freshly cut, it has a metallic luster that quickly dulls to a bluish gray tinge like that of lead. A heavy oxide cmst forms on the metal surface when in contact with air for several days. The metal has a close-packed hexagonal lattice below 230°C, at which point it is transformed to a body-centered cubic lattice. At high pressures, thallium transforms to a face-centered cubic form. The triple point between the three phases is at 110°C and 3000 MPa (30 kbar). The physical properties of thallium are summarized in Table 1. 

Identification. When a solution of ferric chloride is added to a cold, saturated vanillin solution, a blue color appears that changes to brown upon warming to 20°C for a few minutes. On cooling, a white to off-white precipitate (dehydrodivanillin) of silky needles is formed. Vanillin can also be identified by the white to slightly yellow precipitate formed by the addition of lead acetate to a cold aqueous solution of vanillin. 

Dissolved in hot glacial acetic acid, any lead oxide being removed by filtration. White crystals of lead tetraacetate separated on cooling. Stored in a vacuum desiccator over P2O5 and KOH for 24h before use. 

For this reason tribasic lead sulphate, a good heat stabiliser which gives polymer compounds with better electrical insulation properties than lead carbonate, has increased in popularity in recent years at the expense of white lead. Its weight cost is somewhat higher than that of lead carbonate but less than most other stabilisers. This material is used widely in rigid compounds, in electrical insulation compounds and in general purpose formulations. 

Arsenic and selenium, which fall directly below phosphorus and sulfur in the periodic table, are of interest for a variety of reasons. Arsenic is a true metalloid. A metallic form, called gray arsenic, has an electrical conductivity approaching that of lead. Another allotrope, yellow arsenic, is distinctly nonmetallic it has the molecular formula As4, analogous to white phosphorus, P4. Selenium is properly classified as a nonmetal, although one of its allotropes has a somewhat metallic appearance and is a semiconductor. Another form of selenium has the molecular formula Se8. analogous to sulfur. 

The history of lead is almost as ancient as that of tin. In Roman times, lead was formed into pipes that were used for water supplies (hence our word plumbing, derived from the same Latin word, plumbum, that gives us the s Tnbol Pb). Lead is a component of pewter and also was used as a glaze on drinking vessels. White lead, ... 

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