Radio-activity / by E. Rutherford.

  • Ernest Rutherford
Date:
1905
Catalogue details

Licence: Public Domain Mark

Credit: Radio-activity / by E. Rutherford. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    could be observed. For the detection of rjidiuni, the examination of the radio-activity is thus a process nearly a niillion times more sensitive than spectrum analysis. Later observations on the spectrum of radium have been made by Runge*, Exner and Haschekf-, with specimens of radium prepared by Giesel. Crookes;]; has photographed the spectrum of radium in the ultra-violet, while Runge and Precht§, using a highly purified sam})Ie of radium, observed a number of new lines in the spark spectrum. It has been mentioned already that the bromide of radium gives a characteristic pure carmine-red coloration to the Bunsen flame. The flame spectrum shows two broad bright bands in the orange-red, not observed in Demaryay's spectrum. In addition there is a line in the blue-green and two feeble lines in the violet. 14. Atomic weight of radium. Mme Curie has made successive determinations of the atomic weight of the new element with specimens of steadily increasing purity. In the first obser- vation the radium was largely mixed with barium, and the atomic weight obtained was the same as that of barium, 1375. In successive observations with specimens of increasing purity the atomic weights of the mixture were 146 and 175. The final value obtained recently was 225, which may be taken as the atomic weight of radium on the assumption that it is divalent. In these experiments about 01 gram of pure radium chloride was obtained by successive fractionations. The difficulty involved in preparing a quantity of pure radium chloride large enough to test the atomic weight may be gauged from the fact that only a few centigrams of fairly pure radium, or a few decigrams of less concentrated material, are obtained from the treatment of about 2 tons of the mineral from which it is derived. Runge and Prechtji have examined the spectrum of radium in a magnetic field, and have shown the existence of series analogous to those observed for calcium, barium, and strontium. These series. * Eunge, Astrophys. Journal, p. 1, 1900. Annal. d. Phys. No. 10, p. 407, 1903. t Exner and Haschek, Wien. Ber. July 4, 1901. + Crookes, Proc. Roy. Soc. 72, p. 295, 1904. § Eunge and Precht, Annal. d. Phys. xiv. 2, p. 418, 1904. II Eunge and Precht, Phil. Mag. April, 1903.