143 



LEAD. 



scribed at the commencement of this article, and also in NAT. HIST. 

 Div., under LEAD. 



Lead and Iodine form one combination, the protoiodide of lead (Pbl). 

 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 osotpodidct 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. 



Lend and Chlorine form 



Protochloride of lead (PbCU, 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 IB 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 oxychlta-ides of lead are numerous. One occurs native (PbCl,2PbO) 

 [LEAD, Berzelite, in NAT. HIST. Div.] at the Mendip Hills, in Somerset- 

 shire, and is hence frequently called Atendipite. Another, the subject 

 of a patent, and used as a substitute for white lead, is made by acting 

 upon galena ith 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 : 

 2PbCl + CaO = CaCl + PbO, PbCl 



Chloride of lead. Lime. Chloride of calcium. Pattinson's 



oxychloride. 



Catsel or Turner's yellow i an oxychloride of lead, much used as a 

 pigment. It is prepared by heating chloride of ammonium with ten 

 times its weight of litharge. 



fluorine and Lead form a white sparingly soluble fluoride of lead 

 (PbFl). 



Salts of Protoxide of Lead. 



Carbonate of Lead (PbO,C0 2 ). 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. 



\\'ltitr.-lead,a& it occurs in commerce,is generally basic carbonate of lead, 

 containing aboufr? 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 while-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. 



Phonphates 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 rhlfrophosphate of lead (3(3PbO,P0 5 ) + PbCl) is found native. 

 [LEAD, pyromorphite, in NAT. HIST. Div.] 



Sulphate of lead (PbO,SO 3 ) also occurs native. [LEAD, anglesite, in 

 NAT. MIST. Div.] 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 

 noda. It is also slightly soluble in strong nitric 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. 



\itrate* of lead are four : 



ftexbuic nitrate of lead . . . 6PbO, NO,4Aq 



Trinitrate 2(3PbO, NO S ) + SAq 



Dinitratc 2Pb6, NO, + Aq 



Mnnonitratfl .... PbO, SO,, 



The last, or ordinary nitrate of lead is the only one of importance. 



It is readily made by dissolving oxide of lead in diluted nitric acid. 



: 'pointing the solution it crystallises out in more or less opaque 



octohcdra. It is soluble in eiylit times its weight of cold water; paper 



ARTS AM) SCI. DIV. VOL. V. 



LEAD, MEDICAL PROPEKTIK3 OF. 1:8 



or tinder saturated with the solution and dried is thereby rendered 

 exceedingly inflammable. 



Hyponitrates <xPbO,NO t ) and nitrites (zPbO,N0 3 ) of lead are formed 

 when metallic lead is boiled with nitrate of lead. The strength of the 

 solution and the extent of ebullition determines which of these is 

 produced. They are all more or less crystalline. 



Borates of lead result when boracic acid is fused with oxide of lead. 

 One of them enters into the composition of Faraday's optical glass. 



Silicate of lead is abundantly formed in the manufacture of flint 

 [GLASS.] 



Tunystate of lead occurs native. [LEAD, in NAT. HIST. Div.] It 

 forms when ground up with oil a pigment resembling white lead. 



Chromates of lead. The two principal are (1) neutral chromate, 

 PbO,Cr0 3 , and (2) dlchromate (2PbO,Cr0 3 ). 



1. Chromate of lead, or chrome yellon-, occurs under many different 

 names. [COLOURING MATTERS.] It is obtained on adding a clear 

 solution of neutral chromate of potash, soda, or lime, to a solution of 

 nitrate or acetate of lead, well washing the precipitate and drying it 

 out of any possible contact of sulphuretted hydrogen. 



2. Dichromate of lead, or Orange chrome. It is made by boiling 

 white lead in a solution of bichromate of potash, or by fusing yellow 

 chrome with five times its weight of nitre, and well washing the product. 



For a description of the details necessary to be attended to for the 

 production of lead chromes of various shades, see a paper in the ' Phar- 

 maceutical Journal,' vol. xv., pp. 66 and 69. 



Tartrate of lead (2PbO,C 8 H 1 O 10 ). Precipitate acetate of lead dis- 

 solved in water with half its weight of tartaric acid, and wash and dry 

 the precipitate. 



When tartrate of lead is heated in a closed tube it is decomposed, 

 white vapours are evolved, and a mixture of metallic lead and carbon 

 remain in an exceedingly minute state of division. On being thrown 

 out into the air the mixture takes fire spontaneously, and is commonly 

 known as the lead pyrophorous. 



Acetates of lead. [ACETATE.] 



Alloys of lead. [BRITANNIA METAL ; PEWTER ; SOLDERS ; SHOT ; 

 TYPE-METAL.] 



Tests for lead. This metal is recognised in solution by the yellow 

 precipitate of chromate with chromate of potash ; white, soluble in 

 excess with the alkalies; white, insoluble with sulphuric acid or a 

 sulphate. The formation of iodide of lead by adding a few drops of 

 iodide of potassium solution, is perhaps the most characteristic test 

 for lead, as the precipitate dissolves when heated, and is deposited 

 again on cooling in the well-known beautiful golden yellow scales. 

 Sulphuretted hydrogen is, however, the most delicate test for lead. 

 The formation of arborescent crystals of lead, by suspending a piece 

 of zinc in a solution of acetate of lead, is an illustration of how one 

 metal, having more powerful affinities than another, becomes a test 

 for the latter. Thus zinc is a test for lead. 



nation of lead. This is generally effected in the state of sulphate, 

 which contains 68'31 per cent, of metal. 



LEAD, MEDICAL PROPERTIES OF. In a purely metallic state, 

 lead produces no action on the human system, except such as arises 

 from its mechanical properties ; but as soon as it has become oxidised, 

 it can combine with the contents of the stomach, and produce different 

 effects, according to the nature of the substances it meets with, hence 

 even a leaden bullet, swallowed, has given rise to the symptoms charac- 

 teristic of the presence of lead. " In whatever form lead is habitually 

 applied to the body, it is apt to bring on the train of peculiar sym- 

 ptoms : the inhalation of its fumes, the habitual contact of any of its 

 compounds with the skin, the prolonged use of them internally as 

 medicines, or externally as ointments and lotions, and the accidental 

 introduction of them for a length of time, with the food, may, sooner or 

 later, equally induce colica pictonum, or painters' colic. Of all expo- 

 sures none is more rapid or certain than breathing the vapours or dust 

 of the preparations of lead." (Christison.) Thus the workmen at 

 Lead Hills in Lanarkshire are stated never to have the lead-colic until 

 they work at the smelting furnaces. The action of lead on the human 

 frame differs greatly according to the kind of preparation of lead, the 

 quantity employed, the length of time or frequency of exposure to it, 

 and the channel of its introduction into the body, and idiosyncrasy of 

 the individual. If injected into a vein, acetate of lead, even in small 

 dose, will produce almost immediate effects; while if taken into the 

 stomach it is much slower, and a considerable quantity is requisite to 

 produce serious consequences. In the latter instance the effects are 

 both local and remote : " One class of symptoms indicates inflammation 

 of the alimentary canal ; another, spasm of its muscles ; and a third, 

 injury of the nervous system, sometimes apoplexy; more commonly 

 palsy, and that almost always partial and incomplete. Each of these 

 classes of symptoms may exist independently of the other two ; but 

 the last two are more commonly combined." (Christison On Poisons, 

 p. 511.) The rapidity of action is also determined by the solubility of 

 the preparation or salt of lead ; while the degree of effect is also closely 

 connected with the solubility, the more insoluble salts being nearly 

 powerless a circumstance which supplies a convenient mode of dis- 

 arming the others of their virulence by converting them from soluble 

 to insoluble salts. Fatal cases from poisoning by large quantities of 

 the salts of lead are not numerous, as there is in general time to 

 administer antidotes ; but death from the slow and insidious introduc- 



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