and R. Pirret, A. K. Coomaraswamy, etc. From the helium content, E. Rutherford estimated the age to be at least 4x108 yrs.-vide the radioactivity of thorium.

E. H. Buchnen reported that thorianite contained a new element in the analytical arsenic group, and two in the bismuth-cadmium group; C. de B. Evans, that it contained an element in the tin group; and M. Ogawa, that thorianite and molybdenite contained a new element closely allied to molybdenum, and which he called nipponium, Np. This has not yet been confirmed. G. G. Boucher observed in certain specimens of iron and steel a metal resembling molybdenum in some respects but different from it in others. F. G. Ruddock, and C. H. Jones made some observations on this subject; and A. Skrabal and P. Artmann noted a similar metal in ferrovanadium.

W. R. Dunstan and co-workers assume that thorium and uranium dioxides are isomorphous so that thorianite is a solid soln. of the two oxides ThO2 and UO2. The constitution was discussed by G. Wyrouboff and A. Verneuil. G. Troost and L. Ouvrard obtained octahedral crystals of thoria, and W. F. Hillebrand octahedral crystals of uranous oxide belonging to the cubic system, whereas the crystals of thorianite belong to the rhombohedral system. On the other hand, J. Nordenksjöld, C. F. Rammelsberg, and W. F. Hillebrand obtained octahedral crystals of thorianite by fusing the two oxides with borax. The sulphates of uranium and thorium were shown by C. F. Rammelsberg, and W. F. Hillebrand and W. H. Melville, to be isomorphous. It is therefore inferred that the two oxides are probably isomorphous. B. Szilard also assumes that uranium and thorium oxides form solid soln. The twinning of the pseudocubic crystals of thorianite resembles that of fluorspar; but, like the zeolite chabazite, the optical properties correspond with the symmetry of the rhombohedral system, and the angles are probably very close to those of the cube. In view of the fact that both uranous oxide and thoria form octahedral crystals, while a fused mixture of the two yields, on cooling, cubic crystals, it is possible, but not proved, that the pseudocubic thorianite becomes truly cubic at high temp. The values for the sp. gr. of thorianite reported by W. R. Dunstan and co-workers range from 8-0-9.7; the hardness is 7; the index of refraction, 1.8. C. Baskerville found that thorianite is decomposed when heated in a stream of carbonyl chloride.

REFERENCES.

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2 C. Bergemann, Sitzber. Akad. Berlin, 221, 1851; Pogg. Ann., 82. 561, 1851; 85. 558, 1852, Liebig's Ann., 80. 267, 1851; 84. 239, 1852; A. Damour, Compt. Rend. 34. 685, 1852; Ann. Chim. Phys., (3), 35. 241, 1852; N. J. Berlin, Pogg. Ann., 85. 556, 1852; 87. 608, 1852.

3 J. F. Bahr, Efvers. Akad. Förh., 415, 1862; Pogg. Ann., 119. 572, 1863; Chem. News, 8. 175, 185, 1864; Liebig's Ann., 132. 227, 281, 1864; J. Nicklès, Compt. Rend., 57. 740, 1863; Journ. Pharm. Chim., (3), 45. 25, 1864; M. Delafontaine, Arch. Sciences Genève, (2), 18. 369, 1863; Liebig's Ann., 131. 368, 1864; O. Popp, Liebig's Ann., 131. 364, 1864; Trennung des Cers von Lanthan und Didym, Göttingen, 1864.

J. Joly, Radioactivity and Geology, London, 1909; Phil. Mag., (6), 17. 760, 1909; (6), 18. 140, 1909; (6), 20. 125, 353, 1910; A. L. Fletcher, ib., (6), 21. 102, 1911; T. L. Phipson, Chem. News, 43. 145, 1896; G. A. Blanc, Atti Accad. Lincei, (5), 17. i, 101, 1908; (5), 18. i, 241, 1909; Phys. Zeit., 9. 294, 1908; H. Lange, Naturwiss., 82. 1, 1910; R. J. Strutt, Proc. Roy. Soc., 84. A, 195, 1910; G. Hofbauer, Sitzber. Akad. Wien, 116. 267, 1907; H. A. Rowland, Amer. Journ. Science, (3), 41. 243, 1891; Chem. News, 63. 133, 1891; F. W. Clarke and H. S. Washington, The Composition of the Earth's Crust, Washington, 1924; Proc. Nat. Acad. Sciences, 8. 108, 1922; J. H. L. Vogt, Zeit. prakt. Geol., 6. 225, 314, 377, 413, 1898; 7. 10, 274, 1899; L. Moser, Ester. Chem. Ztg., 26. 67, 1923.

5 J. J. Berzelius and H. M. T. Esmark, Pogg. Ann., 15. 633, 1828; H. M. T. Esmark, Mag. Naturwis. Christiana, (2), 2. 277, 1836; J. J. Berzelius, Svenska Akad. Handl., 1, 1829; Pogg. Ann., 16. 395, 1829; H. Rose, ib., 48. 555, 1839; C. Bergemann, ib., 82. 561, 1851; 85. 558, 1852; N. J. Berlin, ib., 85. 555, 1852; H. Dauber, ib., 92. 250, 1854; A. Krautz, 82. 586, 1851; T. Scheerer, ib., 65. 298, 1845; Neues Jahrb. Min., 642, 1843; 569, 1860; Berg. Hütt. Ztg., 19. 124, 1859; A. Breithaupt, ib., 25. 82, 1866; A. Dufrénoy, Traité de minéralogie, Paris, 3. 579, 1847; P. C. Weibye, Karsten's Arch., 22. 538, 1848; A. Damour, Ann. Mines, (4), 5. 587,

VOL. VII.

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1852; Compt. Rend., 34. 685, 1852; Bull. Soc. Min., 1. 32, 1878; F. Pisani, ib., 59. 65, 1904; W. R. Dunstan, Nature, 69. 510, 1904; D. Forbes, Edin. New Phil. Journ., (2), 3. 60, 1856; P. G. Tschernik, Proc. Russ. Min. Soc., 41, 115, 1903; E. Zschau, Amer. Journ. Science, (2), 26. 359, 1858; S. L. Penfield, ib., (3), 24. 252, 1883; W. E. Hidden and J. B. Mackintosh, ib., (3), 41. 438, 1891; G. F. Barker, ib., (4), 16. 161, 1903; B. B. Boltwood, (4), 21. 415, 1906; H. N. McCoy and W. H. Ross, ib., (4), 21, 433, 1906; H. M. Dadourian, ib., (4), 21. 427, 1906; K. A. Hofmann and F. Zerban, Ber., 36. 13093, 1903; J. J. Chydenius, Kemisk Undersökning af Thorjord och Thorsalter, Helsingfors, 1861; Pogg. Ann., 119. 43, 1861; F. Kolbeck and P. Uhlich, Centr. Min., 208, 1904; A. des Cloizeaux, Manuel de minéralogie, Paris, 133, 1862; C. F. Rammelsberg, Handbuch der Mineralchemie, Leipzig, 1. 173, 1875; A. E. Nordenskjöld, Arkiv. Akad. Stockholm, 2. 1, 1905; Geol. För. Förh. Stockholm, 3. 226, 1876; 4. 28, 1879; 9. 26, 434, 1887; S. R. Paykull, ib., 3. 350, 1877; G. Lindström, ib., 5. 270, 1882; A. Hamberg, ib., 16. 327, 1894; M. F. Heddle, Trans. Roy. Soc. Edin., 28. 197, 1877; The Mineralogy of Scotland, Edinburgh, 2. 56, 1901; P. Collier, Journ. Amer. Chem. Soc., 2. 73, 1880; L. F. Nilson, Efvers. Akad. Förh., 7, 1882; Compt. Rend., 95. 784, 1882; Ann. Chim. Phys., (5), 30. 429, 1883; G. Urbain, ib., (7), 19. 202, 1900; W. C. Brögger, Neues Jahrb Min., i, 80, 1883; Zeit. Kryst., 16. 116, 1890; V. Goldschmidt, ib., 45. 490, 1908; G. Woitschach, Abhand. Nat. Ges. Görlitz, 17. 147, 1883; G. Krüss and L. F. Nilson, Ber., 20. 2137, 1887; 21. 558, 1888; G. Krüss and P. Kiese wetter, ib., 21. 2310, 1888; J. F. Kemp, Trans. New York Acad., 13. 76, 1893; J. N. Lockyer, Proc. Roy. Soc., 59. 133, 1895; R. J. Strutt, ib., 76. A, 88, 1905; 80. A, 56, 1907; 82. A, 166, 1909; 84. A, 379, 1910; W. Ramsay, J. N. Collie, and M. W. Travers, Journ. Chem. Soc., 67. 684, 1895; L. Vegard, Phil. Mag., (6), 32. 65, 1916; M. L. Huggins, Phys. Rev., (2), 21. 719, 1923; G. von Hevesy and V. T. Jantzen, Journ. Chem. Soc., 123. 3218, 1923; J. Schilling, Beiträge zur Chemie des Thoriums, Heidelberg, 1901; Zeit. angew. Chem., 15. 921, 1902; Das Vorkommen der Seltenen Erden im Mineralreiche, München, 15, 1904; C. W. Blomstrand, Journ. Prakt. Chem., (2), 29. 200, 1884; W. F. Hillebrand, Bull U.S. Geol. Sur., 113. 41, 1891; Zeit. anorg. Chem., 3. 234, 1893; F. Zambonini, Atti Accad. Napoli, 14. 67, 1908; G. T. Prior, Min. Mag., 15. 78, 1908; W. T. Schaller, Bull. U.S. Geol. Sur., 509, 1912 ; F. Beigerinck, Neues Jahrb. Min. B.B., 11. 448, 1897; B. Szilard, Le Radium, 6. 233, 1909; O. Mann, Beiträge zur Kenntnis verschiediner Mineralien, Leipzig, 1904; Neues Jahrb. Min., ii, 189, 1905; E. Gleditsch, Compt. Rend., 146. 331, 1908; Le Radium, 5. 33, 1908; G. P. Drossbach, Journ. Gasbeleucht., 38. 481, 1895; P. Truchot, Chem. News, 71. 134, 1898; L. Schmelck, Zeit. angew. Chem., 8. 543, 1895; C. R. Böhm, Chem. Ind., 29. 321, 1906; G. G. Boucher, Chem. News, 76. 99, 182, 1897; F. G. Ruddock, ib., 76. 118, 1897; C. H. Jones, ib., 76. 171, 1897; A. L. Fletcher, Scient. Proc. Roy. Dublin Soc., (2), 13. 433, 1913. 6 W. Ramsay, W. R. Dunstan, and G. S. Blake, Proc. Roy. Soc., 76. A, 253, 1905; W. R. Dunstan and B. M. Jones, ib., 77. A, 546, 1906; D. O. Wood, ib., 84. A, 70, 1910; O. Hahn, ib., 78. A, 385, 1906; R. J. Strutt, ib., 76. A, 98, 1905; 84. A, 195, 379, 1910; W. Ramsay, Nature, 69. 533, 559, 1904; W. R. Dunstan, ib., 69. 510, 1904; W. Jakob and J. S. Tolloczko, Bull. Acad. Cracow, 558, 1911; W. F. Hillebrand, Zeit, anorg. Chem., 3. 243, 1893; Bull. U.S. Geol. Sur., 113. 41, 1893; W. Hillebrand and W. H. Melville, ib., 90. 30, 1892; G. von Hevesy and V. T. Jantzen, Journ. Chem. Soc., 123. 3218, 1923; H. Goldschmidt, Zeit. Kryst., 45. 490, 1908; J. Nordenskjöld, Pogg. Ann., 110. 643, 1860; G. Troost and L. Ouvrard, Compt. Rend., 102. 1422, 1886; B. Szilard, ib., 143. 1145, 1906; 145. 463, 1907; E. Gleditsch, ib., 149. 267, 1909; E. Rutherford, Phil. Mag., (6), 12. 348, 1906; F. Soddy and R. Pirret, ib., (6), 20. 345, 1910; A. K. Coomaraswamy, Spolia Zeylamica, 2. iv, 57, 1904; P. Termier, Bull. Soc. Min., 27. 258, 1904; T. L. Phipson, Journ. Gaslight., 87. 380, 1904; 86. 255, 503, 1904; E. H. Buchnen, Chem. News, 94. 233, 1906; Proc. Roy. Soc., 78. A, 385, 1906; C. de B. Evans, Journ. Chem. Soc., 93. 666, 1908; G. Wyrouboff amd A. Verneuil, Bull. Soc. Chim., (3), 21. 118, 1899; Compt. Rend., 128. 1573, 1899; M. Ogawa, Chem. News, 98. 249, 261, 1908; Sakurai's Jubilee Papers, 15, 16, 1908; M. Kobayashi, Science Rep. Tohoku Univ., 1. 201, 1912; C. F. Rammelsberg, Pogg. Ann., 56. 129, 1842; 150. 219, 1873; Handbuch der krystallograpisch-physikalischen Chemie, Leipzig, 1. 441, 1881; C. Baskerville, Science, (2), 50. 443, 1917; A. Schoep, Bull. Soc. Chim. Belg., 32. 274, 1923; G. G. Boucher, Chem. News, 76. 99, 182, 1897; F. O. Ruddock, ib, 76. 118, 1897.

§ 2. The Extraction of Thoria

J. J. Berzelius,1 the discoverer of this earth, extracted it from thorite. The powdered mineral was warmed with hydrochloric acid; some chlorine was evolved, and the mineral gelatinized. The whole was evaporated to dryness to make the silica insoluble. The residue was leached with dil. hydrochloric acid, and the lead, tin, etc., removed from the filtered soln. by hydrogen sulphide. The filtrate was treated with ammonia, and the washed precipitate dissolved in dil. sulphuric acid. The soln. was evaporated at a gentle heat, when thorium sulphate was deposited as a salt sparingly soluble in the hot liquid. The supernatant liquid was poured off, the crystals dried by press. and ignited for thoria. The mother-liquor was

conc. by evap., neutralized with potassium carbonate, and mixed with a boiling sat. soln. of potassium sulphate. The double sulphate which separates on cooling was washed with a sat. soln. of potassium sulphate; dissolved in water; and thorium hydroxide precipitated by ammonia. The presence of manganese imparted a yellow colour to the ignited mass; and J. J. Berzelius found it better to repeat the treatment with sulphuric acid rather than separate the thorium as oxalate. J. J. Chydenius used a similar process.

L. Troost heated a mixture of thorite with finely powdered coal in the electric arc furnace. All but about 1.5 per cent. of silica is volatilized, and this is said to facilitate greatly the subsequent treatment for thoria. O. N. Witt dissolved

the washed precipitate in hydrochloric acid. Oxalic acid was then added so long as precipitation occurred. The washed precipitate was calcined. A little uranium, manganese, and rare earths were contained in the resulting thoria. J. J. Berzelius' process is based on the sparing solubility of thorium sulphate in comparison with the sulphates of the other earths. Modifications were suggested by M. Delafontaine, P. T. Cleve, L. F. Nilson and co-workers. J. J. Berzelius, and J. J. Chydenius also, purified the thoria by a process based on the sparing solubility of the double salt-potassium thorium sulphate-in a sat. soln. of potassium sulphate. The yttria earth sulphates are fairly soluble and are readily removed. Processes for the removal of the ceria earths based on the solubility of thorium oxalate in ammonium oxalate or ammonium carbonate, under conditions where the other oxalates are but sparingly soluble, have been given by A. Damour, R. Bunsen, H. Moissan and A. Étard, P. Jannasch and co-workers, J. Lesinsky, and G. Urbain. Vide the rare earths. V. I. Spitzin has measured the solubility of thorium oxalate in various soln.

J. J. Chydenius extracted thoria from euxenite by digesting the powdered mineral with conc. sulphuric acid; the product was dissolved in cold water and the soln, boiled for some days. The greater part of the titanium and columbium was precipitated. The thoria was then extracted from the filtrate by J. J. Berzelius' process. J. L. Smith extracted the thoria from samarskite by digesting the powdered mineral with cold conc. hydrofluoric acid, finishing off the operation by warming the mass. The rare earth fluorides, thorium fluoride, and uranium fluoride remain undissolved; the columbium, tantalum, iron, and manganese pass into soln. The insoluble mass is digested with sulphuric acid, and the soln. then treated for thoria by the oxalate process. G. Siebert and E. Korten treated the raw material with halogens in the presence of carbon at a high temp.

According to C. R. Böhm, most of the thorium compounds in commerce are extracted from monazite sand as described in connection with the rare earths. The deposits in the vicinity of Bahia, Espirito Santo, and Rio de Janeiro on the Brazilian coast, have been worked for many years. The deposits in North and South Carolina in the United States, and the deposits at Travancore, Southern India, are also worked. The monazite sands contain 2-60 per cent. of monazite. The monazite from Brazil contains 5-6 per cent. of thoria, while, according to E. White, Travancore monazite has 6-14 per cent. of thoria. The grains of monazite in the sand are associated with quartz, ilmenite, garnet, rutile, zircon, hornblende, etc. The sand is usually conc. until it contains at least 90 per cent. monazite.

The concentration of monazite sand has been discussed by H. B. C. Nitze, F. Freize, etc. In the wet process of extraction the sand is run with a stream of water on to one corner of a rectangular table. The table is so tilted that the material travels diagonally across it; the passage of the particles across the table is assisted by the shaking or jigging motion mechanically imparted to the table. The particles roughly range themselves in the order of their sp. gr. The weakness of the process is the tendency for aggregates of small particles of high sp. gr. to behave like a smaller number of large particles of small sp. gr. Pneumatic processes can be used in which blasts of air take the place of currents of water. initial concentration may be performed by a wet process, and the conc. then

The

B,

Bz

H

raised by electro-magnetic separation. Electro-magnetic separation is considered to be the most satisfactory method of obtaining a high-grade monazite. In this process, a belt, B1, Fig. 1, carries the well-dried sand from a hopper, H, and projects it against a second belt, B2, which travels just beneath the poles, P, P, P, of a powerful electro-magnet. The constituent minerals of the sand are attracted towards the magnet in varying degrees and fall into collecting boxes, A, B, arranged in the order of their magnetic permeability. The non-magnetic discharge collects in the box C. Two repetitions of the process will usually give a concentrate with 90-95 per cent. of monazite. The subject is discussed in C. G. Gunther's Electromagnetic Ore Separation (New York, 1909), and D. Korda's La séparation électromagnétique et électrostatique des minerais (Paris, 1905).

A B C

FIG. 1.-Magnetic Concentration of Monazite
Sand (Diagrammatic).

C. R. Böhm thus outlines the process employed for extracting thorium from monazite concentrates. The conc. monazite may or may not require a preliminary grinding. It is then mixed with about twice its weight of conc. sulphuric acid (sp. gr. 1.84), and heated in cast-iron pans until the white pasty mass of sulphates, etc., is soluble in water, and no yellow grains of monazite remain undissolved. The product is then run into a leaden vat and the whole is well stirred. The mixture is allowed to stand in order to allow the insoluble or unattacked minerals to settle. The soln. containing the rare-earth phosphates is syphoned off. The ratio of thoria to the rare earths in the soln. is about 1: 12. Thorium is more basic than the rare earths, so that when the acid soln. is gradually neutralized by adding ammonia, alkali hydroxide or carbonates, or, more usually, magnesite, thorium phosphate accumulates in the first precipitate. The thorium phosphate is filtered off, dissolved in the minimum quantity of acid, and the process repeated. This raises the proportion of thoria to the rare earths to about 4:1. The product is next to be freed from phosphoric acid and the remaining ceria earths.

Several processes have been suggested; but many of them are too expensive for commercial work. The actual procedure is kept a secret. In the oxalate process described by C. R. Böhm, the acid soln. of the phosphate is treated with a hot soln. of oxalic acid; the precipitated oxalates are washed, digested with a soln. of sodium carbonate, as recommended by O. N. Witt, and precipitated from the soln. with sodium hydroxide; or the mixed oxalates are treated with a warm soln. of ammonium oxalate, as recommended by R. Bunsen, when all the thorium oxalate dissolves and only small quantities of the other oxalates pass into soln., and these are nearly all precipitated when the soln. is diluted. O. N. Witt recommends applying the sodium thiosulphate precipitation-vide infra-before the oxalate treatment. The Société Minière et Industrie Franco-Brésilienne precipitated the thorium, cerium, etc., as anhydrous sulphates from the sulphuric acid soln. of monazite, and removed the phosphoric acid by centrifuging. M. Fronstein and J. Mai, J. W. Ling, G. Thesen, H. Moissan and A. Étard, G. Urbain, etc., used modifications of the oxalate process.

B. Kossmann treated the sulphuric acid soln. of monazite with ammonia; dissolved the precipitate in hydrochloric acid; sat, the feebly acid soln. with hydrogen sulphide; decanted the clear liquid from the precipitated aluminium and iron phosphates and tin sulphide, and treated the soln, with hydrogen dioxide, ammonia, and ammonium citrate. The precipitate contained aluminium phosphate mixed with thorium hydroxide-freed from didymium and cerium compounds. The precipitate was dissolved in nitric acid, and the thorium purified by the oxalate process, or by the acetate process. In F. Haber's form of the acetate process,

the impure hydroxide is dissolved in acid, and the thorium precipitated from neutral soln. by sodium acetate. The treatment is repeated until the purification has been carried far enough. The results are said to be good, but too costly for large-scale work.

G. Wyrouboff and A. Verneuil recommend the following process:

The mineral is dissolved in the usual way, and the soln., which must contain sufficient acid to prevent precipitation of the phosphates, is precipitated with half the quantity of oxalic acid necessary for complete precipitation. The oxalates are washed until free from phosphoric acid, converted into carbonates by means of a hot soln. of sodium carbonate (1:10), and some sodium hydroxide added to ensure complete precipitation of the thorium. The carbonates are washed until free from oxalic acid, dissolved in just the necessary quantity of hydrochloric acid, and mixed with successive small quantities of barium peroxide suspended in water until the liquid gives no precipitate with hydrogen dioxide. The precipitated peroxide contains all the thorium, together with 20-30 per cent. of impurities; it is washed and dissolved in cold conc. hydrochloric acid, barium eliminated by means of sulphuric acid, enough water added to yield a soln. containing 15 per cent. of acid, and the bases precipitated with oxalic acid. The oxalates are washed, and treated with a highly conc. soln. of ammonium carbonate mixed with sufficient ammonia to form the normal salt. By two or three successive treatments, all the thorium is dissolved, and the soln. is precipitated by means of sodium hydroxide, the precipitate well washed and dissolved in not more than the requisite quantity of nitric acid, and the liquid poured into sufficient water to yield a soln. containing not more than 2 per cent. of thorium. Excess of hydrogen dioxide is then added, and the precipitate is well washed. From this point, all the reagents must be pure. The precipitate is dissolved in nitric acid and reprecipitated with hydrogen dioxide in order to eliminate all the cerium. It is next dissolved in hydrochloric acid, precipitated with oxalic acid, and the oxalate decomposed by pure sodium hydroxide. After careful washing, the precipitate is again dissolved in hydrochloric acid and precipitated with ammonia. This final precipitate is well washed, dissolved in nitric acid, and the nitrate crystallized.

C. R. Böhm removed the phosphates by fusing the precipitate with sodium carbonate and leaching the mass with water. The phosphates and silicates pass into soln., while the thoria and rare earth oxides remain. W. Buddeus and L. Preussner used alkali hydroxides in place of the carbonate. L. Weiss heated a mixture of monazite with carbon in an electric furnace whereby carbides and phosphides are formed. The mass was treated with hydrochloric acid, and the phosphorus escaped as phosphine. C. Baskerville proposed to volatilize the phosphorus by heating a mixture of monazite, coke, calcium oxide, and fluorspar in an electric furnace until the fumes of phosphorus were no longer evolved. When the cold mass is treated with water, acetylene is evolved. The powder is well washed to remove the lime, and then dissolved in hydrochloric acid for the separation of thorium, etc.

The purification of thoria.-The thoria contains a little sulphate, phosphate, calcium oxide, alkalies, zirconia, and rare earths. The usual methods of purification are (i) the fractional crystallization of the sulphates; (ii) the fractional soln. of the oxalates; or (iii) the separation by double alkali carbonates. There are also a number of processes more or less adapted for special purposes, but which are usually too expensive for large-scale operations. These processes have been discussed in a special section dealing with the separation of the rare earths. The oxalate process is based on the property possessed by thorium oxalate of forming a soluble double salt with ammonium oxalate, while the cerium earth oxalates are but sparingly soluble in that medium. The relative solubilities of the various oxalates are:

The method-vide supra-was employed by B. Brauner, C. Böttinger, P. Jannasch and co-workers, C. Winkler, J. Lesinsky, E. Rimbach and A. Schubert, etc.

The sulphate process is based upon the property which thorium possesses of forming a number of hydrated sulphates, some of which differ so much in solubility from the ceria earths that a separation can be readily obtained. The process was