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A. M. Anderson, Special Report on Dangerous and Injurious Processes in the Enamelling and Tinning of Metals, London, 1902; G. van Eijk, Chem. Weekbl., 2. 541, 1905; T. E. Thorpe and T. Oliver, Lead Compounds in Pottery, London, 1899; T. E. Thorpe, Report of the Government Laboratory on the Question of the Employment of Lead Compounds in Pottery, London, 1901; L. Spiegel, Naturwiss., 1. 374, 1913; E. Wutzdorff, Die in elektrischen Akkumulatoren Fabriken beobachteten Gesundheits schädigunge und die zur Verhüting derselben erforderlichen Massnahmen, Berlin, 1898; Arb. Kaiser. Gesundheitsamte, 15. 154, 1898; L. Petrik, Sprech., 47. 1, 1914; 53. 405, 1920; R. Berge, ib., 47. 99, 113, 1914; J. Dorfner, ib., 47. 390, 1914; L. J. Boyd, Journ. Amer. Inst. Homeopathy, 14. 1001, 1922; M. Willenz, Bull. Assoc. Belg., 15. 230, 1901; G. E. Duckering, The Cause of Lead Poisoning in the Tinning of Metals, London, 1908; A. Sellers, Journ. Ind. Hyg., 2. 361, 1921; J. Grönberg, Finsk. Läkaresällskapets Handl., 63. 429, 1922; R. Franz, Ker. Rund., 31. 219, 1923; L. Petri, Biochem. Zeit., 21. 551, 1909; S. J. Knott, Chem. News, 34. 196, 1876; Lancet, ii, 531, 1876; G. Johnson, Pharm. Journ., (3), 1. 426, 1870; Brit. Med. Journ., ii, 325, 1870; E. Behrle, Zeit. angew. Chem., 37. 1023, 1924; F. H. de Balsac, A. Lafont, and A. Feil, Bull. Méd., 3, 1925; Chim. Ind., 15. 225, 1926; J. C. Aub, Lead Poisoning, Baltimore, 1926; Anon., Bleivergiftungen in hüttenmännischen und gewerblichen Betrieben Ursachen und Bekämpfung, Wien, 1905; R. Fischer, Mitt. Inst. Gew. Hyg., 169, 1912; P. Schmidt, Bleivergiftungen und ihre Erkennung, Berlin, 1907; J. F. Sacher, Der Völkerbund gegen die Bleiindustrie, Dusseldorf, 1921; J. Rambousek, Chem. Ztg., 37. 181, 1913; Zentr. Gew. Hyg., 2. 87, 121, 233, 1914; L. Teleky, ib., 2. 161, 193, 1913; 225, 1914; S. Böttrich, ib., 1. 158, 1913; 4. 58, 1916; J. Schönfeld, ib., 9. 3, 256, 1921; Farbe Lack, 297, 1925; A. Müller, Zentr. Gew. Hyg., 1. 529, 1913; 2. 223, 1914; L. Grobe, ib., 9. 52, 1921; F. Koelsch, ib., 1. 156, 1913; K. B. Lehmann, ib., 10. 46, 1922; Die deutsche Bleifarbenindustrie vom Standpunkte der Hygiene, Berlin, 1925; K. Hamel, Deut. Arch. Klin. Med., 67. 357, 1900; A. Trautmann, Münch. Med. Wochschr., 1371, 1909.

21 P. Orfila, Heller's Arch., 376, 1847; R. V. Tuson, Veterinarian, 38. 6, 217, 220, 421, 1865; E. Harnack, Deut. Med. Wochschr., 23. 8-10, 1897; A. Gusserow, Virchow's Arch., 21. 443, 1861; W. Rosenstein, ib., 39. 1, 174, 1867; Arch. Path. Pharm., 40. 363, 1898; E. Heubel, Pathogenese und Symptome der chronischen Bleivergiftung, Berlin, 1871; R. Stockman and F. J. Charteris, Journ. Path. Bact., 9. 202, 1903; R. T. H. Laennec, Traité de l'auscultation médiate, Paris, 1831; G. Andral and J. Gavarret, Ann. Chim. Phys., (2), 75. 309, 1840; J. C. Aub, P. Reznikoff, and D. E. Smith, Journ. Exp. Med., 40. 151, 173, 1924; J. C. Aub and P. Reznikoff, ib., 40. 189, 1924; J. C. Aub, A. S. Minot, L. T. Fairhall, and P. Reznikoff, Journ. Amer. Med. Assoc., 83. 588, 1924; H. Burton, Gaz. Méd. Paris, (2), 8. 470, 1840.

22 H. Devaux, Compt. Rend., 133. 58, 1901; J. Stoklasa, ib., 156. 153, 1913; A. Lumière and J. Chevrotin, Bull. Gén. Thérap., 165. 959, 1913; T. Messerschnidt, Zeit. Hyg., 82. 289, 1916; L. Bitter, ib., 69. 483, 1912; G. Sonntag, Arb. Kaiser. Ges. Amt., 49. 502, 1914; R. Klein, Dingler's Journ., 221. 287, 1876; Chem. Ackersmann, 21. 248, 1875; U. Varvaro, Staz. Sperim. Agrar. Ital., 45. 917, 1912; A. Stutzer, Journ. Landw., 64. 1, 1916; R. Stockmann and F. J. Charteris, Journ. Rath. Bact., 9. 202, 1903; A. Stockhardt, Arch. Pharm., 200. 170, 1872; A. Schmidt, Centrb. Bakteriol., 12. 93, 1904; 14. 289, 1905; 15. 349, 1906; T. Bokorny, ib., 35. 118, 1912; P. Eisenberg, ib., 82. 69, 1918.

23 G. O. Hiers, Journ. Ind. Eng. Chem., 15. 467, 1923.

24 S. Cowper-Coles, Metal Ind., 4. 308, 1912; M. A. Schoop, Met. Chem. Engg., 11. 89, 1913.

25 J. H. Frydlender, Rev. Prod. Chim., 28. 685, 1925; G. L. Clark and W. C. Thee, Journ. Ind. Eng. Chem., 17. 1219, 1915; G. L. Clark, E. W. Brugmann, and W. C. Thee, ib., 17. 1226, 1925; G. L. Wendt and F. V. Grimm, ib., 16. 890, 1924; Anon., ib., 18. 432, 1926; T. Midgley, ib., 17. 752, 1925.

26 A. Kinsel, Chem. Met. Engg., 32. 873, 1925.

§ 6. The Valency and Atomic Weight of Lead

According to H. E. Roscoe and A. Harden,1 in a note-book dated March, 1804, J. Dalton wrote 105 for the at. wt. of lead when that of oxygen is 5.5; and this number becomes 305 when the at. wt. of oxygen is 16. In his later work, J. Dalton adopted 90 for the at. wt. of lead when that of oxygen is 7, or 206 if oxygen is 16. In 1811, J. J. Berzelius calculated from the ratio Pb : PbO, the at. wt. 206.5 when the at. wt. of oxygen is 16; from the ratio PbS: PbSO4, 209-9; from the ratio Pb: PbSO4, 207-6; and from the ratio PbO: PbSO4, 207.98. At first he was not very clear whether to represent what is now called lead monoxide, PbO, by the formula PbO, Pb2O3, PbO2, PbO3, or Pb04. After the sp. ht. rule, and the isomorphism rule had been developed, he adopted the now accepted formula PbO. This made the at. wt. of lead approximate 207. Lead ordinarily behaves as a

bivalent element giving salts isomorphous with those of the bivalent alkaline earth. 601 metals. So much do the normal lead salts resemble those of the alkaline earths that A. Baudrimont suggested that lead should be included in that family. For the genetic connection of lead with radium which in turn belongs to the alkaline earth family of metals, vide infra. Lead can also behave as a quadrivalent element as is evidenced by the higher oxide, PbO2; lead tetramethide, Pb(CH3)4, which has a vap. density of 9.52 (air unity) in agreement with the calculated value 9.25; and the isomorphism of the complex fluorides and chlorides-3KF.HF.PbF, and 3KF.HF.SnF4; and R2PbCl, and R2SnCle, where R represents NH4 or Cs. These observations agree with the position of lead in the tin family in the periodic table. G. Oddo also emphasized the family relations of lead, tin, and germanium. E. W. Wetherell discussed the position of lead in the periodic table.

There is some evidence of univalent lead-vide lead suboxide and the subsalts of lead. According to H. G. Denham and A. J. Allmand, in attempting to measure the hydrolysis of lead salts by the hydrogen electrode, abnormally high values are obtained. This is not due to the separation from the soln. of a metal, say silver, more noble than hydrogen; nor to the deposition of lead on the electrode in such a way that the hydrogen electrode acted as a cathode, nor to the formation of a lead-platinum alloy. The potential depended on the rate at which hydrogen was bubbled through the soln. and it was assumed that the action on the surface film involves a reduction of bivalent lead: PbCl2+H÷PbCl+HCl; the faster the stream of hydrogen, the more quickly was the free acid so produced carried into the main bulk of the liquid, and the lower the potential. E. Bose attributed a discrepancy in the silver voltameter to the formation of subvalent ions; and T. W. Richards and co-workers, in the copper voltameter, to the formation of cuprous salts in soln. A hot soln. of a lead salt can dissolve the metal, and give it up again on cooling. A piece of lead in a soln. of lead acetate, maintained at two different temp., forms a thermo-cell; the current flows from the hot soln. to the cold one, and causes a deposition of spongy lead at the cold end of the piece of lead. There is also a series of compounds in which lead appears to act as a tervalent element, judging by the analogy of the products prepared by E. Krause, with triphenylmethyl-vide valency of carbon. tricyclohexyl, Pb(C6H11)'3, by the action of lead chloride on a soln. of magnesium Thus, E. Krause made lead cyclohexyl bromide in dry ether. The corresponding lead triphenyl, Pb(C&H5)3; lead tri-o-tolyl, Pb(C7H7); lead tri-p-tolyl, Pb(C7H7)3; and lead tri-p-xylyl, Pb(CgHg)3, have been examined by E. Krause and G. G. Reissaus. According to W. Esch, lead exhibits a still higher valency in the acid sulphate, H2Pb(SO4)3, which may be regarded as hydrotrisulphatometaplumbic acid.

:

The at. wt. of lead calculated from J. J. Berzelius' values for the ratio Pb : PbO, obtained by converting the metal to the nitrate, and calcining the product for the oxide, is 206-5; from the ratio PbO: Pb obtained by reducing the heated oxide in hydrogen, 207-06-207-14; and from the ratio PbS: PbSO4, obtained by treating the sulphide with aqua regia, he obtained 209-9. T. Anderson's values for Pb(NO3)2 PbO give 207-360. J. J. Berzelius converted the metal into sulphate, and his values for the ratio Pb: PbSO4, furnish the at. wts. 206-97 and 207-6 ; T. Turner's values, 207-05; and J. S. Stas, 206-93. J. J. Berzelius also converted the oxide into sulphate and from the ratio PbO: PbSO4, it follows that the at. wt. is 207-5-207-98; and T. Turner's values gave 207-64. The values of the last-named for the ratio Pb(NO3)2 : PbSO4 gave 204-2, and J. S. Stas', 206-46. From J. S. Stas' value for the ratio Pb: Pb(NO3)2, the at. wt. is 206-80-206-82. J. J. Berzelius measured the ratio PbO: CO2, and the results correspond with the at. wt. 206-98. T. Thomson made some observations on the at. wt. of lead. J. C. G. de Marignac converted lead into the chloride, and obtained the ratio Pb: PbCl2, from which the at. wt. is 206-87; he also analyzed the chloride for the ratio PbCl2 : 2AgCl, and the results give 206-85, while G. P. Baxter and J. H. Wilson's results give 207-103; and G. P. Baxter and F. L. Grover's gave 207-23. From the ratio