Page:EB1911 - Volume 22.djvu/819

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sufficiently to emerge on the side of incidence. This scattering of the β rays has been investigated by Eve, McLennan, Schmidt, Crowther and others. It has been found that the scattering for different chemical elements is connected with their atomic weight and their position in the periodic table. McCelland and Schmidt have given theories to accourf for the absorption of β rays by matter. The whole problem of absorption and scattering of particles by substances is very complicated, and the question is still under active examination and discussion. The negative charge carried by the β rays has been measured by a number of observers. It has been shown by Rutherford and Makower that the number of β particles expelled per second from one gram of radium in equilibrium is about that to be expected if each atom of the β ray products in breaking up emits one β particle.

Heat Emission of Radioactive Matter.—In 1903 it was shown by Curie and Laborde (52) that a radium compound was always hotter than the surrounding medium, and radiated heat at a constant rate of about 100 gram calories per hour per gram of radium. The rate of evolution of heat by radium has been measured subsequently by a number of observers. The latest and most accurate determination by Schweidler and Hess, using about half a gram of radium, gave 118 gram calories per gram per hour (53). There is now no doubt that the evolution of heat by radium and other radioactive matter is mainly a secondary phenomenon, resulting mainly from the expulsion of α particles. Since the latter have a large kinetic energy and are easily absorbed by matter, all of these particles are stopped in the radium itself or in the envelope surrounding it, and their energy of motion is transformed into heat. On this view, the evolution of heat from any type of radioactive matter is proportional to the kinetic energy of the expelled a particles. The view that the heating effect of radium was a measure of the kinetic energy of the α particles was strongly confirmed by the experiments of Rutherford and Barnes (54). They showed, that the emanation and its products when removed from radium were responsible for about three-quarters of the heating effect of radium in equilibrium. The heating effect of the radium emanation decayed at the same rate as its activity. In addition, it was found that the ray products, viz. the emanation radium A and radium C, each gave a heating effect approximately proportional to their activity. Measurements have been made on the heating effect of uranium and thorium and of pitchblende and polonium. In each case, the evolution of heat has been shown to be approximately a measure of the kinetic energy of the α particles.

Experiments on the evolution of heat from radium and its emanation have brought to light the enormous amount of energy accompanying the transformation of radioactive matter where α particles are emitted. For example, the emanation from one gram of radium in equilibrium with its products emits heat initially at the rate of about 90 gram calories per hour. The total heat emitted during its transformation is about 12,000 gram calories. Now the initial volume of the emanation from one gram of radium is .6 cubic millimetres. Consequently one cubic centimetre of emanation during its life emits 2 × 107 gram calories. Taking the atomic weight of the emanation as 222, one gram of the emanation emits during its life 2 × 109 gram calories of heat. This evolution of heat is enormous compared with that emitted in any known chemical reaction. There is every reason to believe that the total emission of energy from any type of radioactive matter during its transformation is of the same order of magnitude as for the emanation. The atoms of matter must consequently be regarded as containing enormous stores of energy which are only released by the disintegration of the atom.

A large amount of work has been done in measuring the amount of the thorium and radium emanation in the atmosphere, and in determining the quantity of radium and thorium distributed on the surface of the earth. The information already obtained has an important bearing on geology and atmospheric electricity.

References.—1. H. Becquerel, Comptes Rendus, 1896, pp. 420, 501, 559, 689, 762, 1086; 2. Rutherford, Phil. Mag., Jan. 1899; 3. Mme Curie, Comptes Rendus, 1898, 126. p. 1101; M and Mme Curie and G. Bémont, ib., 1898, 127. p. 1215; 4. Mme Curie, ib., 1907, 145. p. 422; 5. Thorpe, Proc. Roy. Soc., 1908, 80. p. 298; 6. Giesel, Phys. Zeit., 1902, 3. p. 578; 7. Giesel, Annal. d. Phys., 1899, 69. p. 91; Ber., 1902, p. 3608; 8. Rutherford and Boltwood, Amer. Journ. Sci., July 1906; 9. Debierne, Comptes Rendus, 1899, 129. p. 593; 1900, 130. p. 206; 10. Giesel, Ber., 1902, p. 3608; 1903, p. 342; 11. Marckwald, ib., 1903, p. 2662; 12. Mme Curie and Debierne, Comptes Rendus, 1910, 150. p. 386; 13. Boltwood, Amer. Journ. Sci., May 1908; 14. Rutherford, Phil. Mag., Feb. 1903, Oct., 1906; 15. Rutherford, ib., Jan. 1900; 16. Rutherford and Soddy, ib., May 1903; 17. Rutherford and Soddy, ib., Nov. 1902; 18. M and Mme Curie, Comptes Rendus, 1899, 129. p. 714; 19. Rutherford, Phil. Mag., Jan. and Feb. 1900; 20. Rutherford and Soddy, ib., Sept. and Nov. 1902, April and May 1903; Rutherford, Phil. Trans., 1904, 204A. p. 169; 21. Russ and Makower, Proc. Roy. Soc., 1909, 82A. p. 205; 22. Hahn, Phys. Zeit., 1909, 10. p. 81; 23. Rutherford, Phil. Mag., Nov. 1904, Sept. 1905; 24. Meyer and Schweidler, Wien. Ber., July 1905; 25. Antonoff, Phil. Mag., June 1910; 26. Cameron and Ramsay, Trans. Chem. Soc., 1907, p. 1266; Rutherford, Phil. Mag., Aug. 1908; 27. Cameron and Ramsay, Proc. Roy. Soc., 1908, 81A. p. 210; Rutherford and Royds, Phil. Mag., 1908, 16. p. 313; Royds, Proc. Roy. Soc., 1909, 82A. p. 22; Watson, ib., 1910, 83A. p. 50; 28. Rutherford, Phil. Mag., 1909; 29. Gray and Ramsay, Trans. Chem. Soc., 1909, pp. 354, 1073; 30. Rutherford and Soddy, Phil. Mag., Sept. and Nov. 1902; 31. Hahn, Proc. Roy. Soc., March 1905; Phil. Mag., June 1906; Ber., 40. pp. 1462, 3304; Phys. Zeit., 1908, 9. pp. 245, 246; 32. Hahn, Phil. Mag., Sept. 1906; 33. Godlewski, ib., July 1905; 34. Boltwood, ib., April 1905; 35. Strutt, Trans. Roy. Soc., 1905A.; 36. McCoy, Ber., 1904, p. 2641; 37. Soddy, Phil. Mag., June 1905, Aug. 1907, Oct. 1908, Jan. 1909; 38. Boltwood, Amer. Journ. Sci., Dec. 1906, Oct. 1907, May 1908, June 1908; 39. Boltwood, ib., April 1908; 40. Boltwood, ib., Oct. 1905, Feb. 1907; 41. Rutherford and Geiger, Proc. Roy. Soc., 1908, 81A. p. 141; 42. Rutherford and Royds, Phil. Mag., Feb. 1909; 43. Dewar, Proc. Roy. Soc., 1908, 81A. p. 280; 1910, 83. p. 404; 44. Boltwood and Rutherford, Manch. Lit. and Phil. Soc., 1909, 54. No. 6; 45. Bragg and Kleeman, Phil. Mag., Dec. 1904, Sept. 1905; 46. Rutherford, ib., Aug. 1906; 47. Geiger, Proc. Roy. Soc., 1910, 83A. p. 505; 48. Geiger, ib., 1910, 83A. p. 492; 49. Rutherford and Geiger, ib., 1908, 81A. pp. 141, 163; 50. Crookes, ib., 1903; 51. Regener, Verhandl. d. D. Phys. Ges., 1908, 10. p. 28; 52. Curie and Laborde, Comptes Rendus, 1904, 136. p. 673; 53. Schweidler and Hess, Wien. Ber., June 1908, 117; 54. Rutherford and Barnes, Phil. Mag., Feb. 1904.

General treatises are: P. Curie, Œuvres, 1908; E. Rutherford, Radioactive Transformations, 1906; F. Soddy, Interpretation of Radium, 1909; R. J. Strutt, Becquerel Rays and Radium, 1904; W. Makower, Radioactive Substances, 1908; J. Joly, Radioactivity and Geology, 1909. See also Annual Reports of the Chemical Society.

(E. Ru.)

RADIOLARIA, so called by E. Haeckel in 1862 (Polycystina, by C. G. Ehrenberg, 1838), the name given to Marine Sarcodina, in which the cytoplasmic body gives off numerous fine radiating pseudopods (rarely anastomosing) from its surface, and is provided with a chitinous “central capsule,” surrounding the inner part which encloses the nucleus, the inner and outer cytoplasm communicating through either one or three apertures or numerous pores in the capsule. The extracapsular cytoplasm is largely transformed into a gelatinous substance (“calymma”), through which a granular network of plasm passes to form a continuous layer bearing the pseudo pods at the surface; this gelatinous layer is full of large vacuoles, “alveoli,” as in other pelagic Sarcodina (Heliozoa, q.v.), Globigerinidae, &c., among Foraminifera (q.v.). The protoplasm may contain oil-globules, pigment-grains, reserve-grains and crystals. There is frequently a skeleton present, either of silica (pure or containing a certain amount of organic admixture), or of “acanthin” (possibly a proteid, allied to vitellin, but regarded by W. Schewiakoff as a hydrated silicate of calcium and aluminium); never calcareous or arenaceous. The skeleton may consist of spicules, isolated or more or less compacted, or form a latticed shell, which, in correlation with the greater resistance of its substance, is of lighter and more elegant structure than in the Foraminifera. The alveoli contain a liquid, which, as shown by Brandt, is rich in carbon dioxide, and in proportion to its abundance may become much lighter than sea-water; and possibly the gelatinous substance of the calymma is also lighter than the medium. In Acantharia the protoplasm at the base