![]() Thomson, Cathode Rays, Philosophical Magazine, 1897, Classic Papers on Carmen Giunta's web site Johnstone Stoney, Of the Electron, or Atom of Electricity, Philosophical Magazine, 1894, posted on ChemTeam web site. Svante Arrhenius, On the Dissociation of Substances Dissolved in Water, Seitschrift für Physikalische Chemie, 1887, via Google Books.(Plum pudding is a common English steamed bread pudding well mixed with various nuts and fruits) References: Negative electrons are like raisins evenly distributed through positively charged pudding. Thomson and William Thomson (Lord Kelvin) proposed a model for atoms suggesting that atoms are built like plum pudding. Thomson concluded that electrons are probably a fundamental part of all atoms. Thomson subsequently found that identical electrons were obtained from every kind of metal electrode he tried. Thomson proposed electric corpuscle as the name of particles constituting cathode rays, but Goldstein's name electron became popular instead. The q/m ratio was consistent with a mass less than 1/1000 that of the lightest atom, Hydrogen. Then combining equations for electric and magnetic forces, he calculated the speed of the negatively charged cathode rays, and the ratio of their electric charge to mass (q/m). Adjusting the strength of an electric field created by charged metal plates inside his apparatus ( shown below ↓) to just counteract a magnetic field created by two magnetic coils of wire placed outside straddling the apparatus, Thomson was able to cancel the effects of the two forces so that a beam of cathode rays travelled straight through his apparatus. Having done so, he was finally able to deflect the cathode rays by an electric field. Thomson baked the tubes to release residual gases prior to final evacuation. In 1897 Joseph John Thomson ( b1856, d1940, ←photograph at left) at Cambridge, suspected that residual air stuck to the internal tube parts might shield the rays from electric fields thus blocking the expected attraction or repulsion by charged plates. ![]() Thus gases ( at least at very low pressures), like solutions, do use ions to conduct electricity. In 1897 Wilhelm Wien ( b1864, d1928) measured the mass of the positively charged canal rays, finding they have the mass of ions. In 1891 George Johnstone Stoney ( b1826, d1911) proposed the unit of charge should be called an electron. ![]() Behind holes bored in the cathode he found opposite charged (+) radiation in 1886 for which he proposed the name canal rays. Still the atomic theory continued to remain controversial for many chemists and physicists until well after 1900.Īfter Arrhenius introduced his theory about charged ions, many suspected that the current in Geissler's tubes is likely carried by charged atoms moving in the near vacuum similar to the current carried in solutions.Įugen Goldstein ( b1850, d1930) proposed the negative (–) radiation be called cathode rays. Arrhenius's theory eliminated much of the confusion about the properties of solutions and indefinite compounds which had discouraged Mendeléeff and others from fully accepting the atomic theory. The ions explained electrical conduction of solutions of salts, anomalies in osmosis, and similarities in the heats of neutralization. In 1883 Svante Arrhenius ( b1859, d1927, ←photograph at left) presented to the Swedish Academy of Sciences his theory that neutrally charged salts dissociate when dissolving to form electrically charged atoms or groups of atoms called ions. ( As a result they were called Crookes rays by many scientists.) He believed the rays were negatively charged material, perhaps a fourth state of matter. ![]() In 1874 William Crookes turned a small paddle wheel with the discharge. The location of the shadows suggested that the sparks originated from the negative electrode and moved towards the positive electrode. Hittorf noted that the electric discharge in Geissler tubes produces shadows behind obstacles. But attempts to demonstrate such electrical deflection had all failed. But such charged bodies should also be deflected by metal plates charged with electricity. This was consistent with the idea that moving bodies carrying electric charge should be deflected in a magnetic field. The fluorescence could be moved with a magnet. Julius Plücker ( b1801, d1868) noted fluorescence on the glass when an electric spark passed through Geissler tubes. He produced electric discharge between electrodes sealed in evacuated glass tubes. Between 18 Heinrich Geissler ( born 1814, died 1859) developed a Mercury diffusion pump producing high vacuums. ![]()
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