Inorganic chemistry for advanced students / by Sir Henry Roscoe and Arthur Harden.

  • Roscoe, Henry E. (Henry Enfield), 1833-1915.
Date:
1910
Catalogue details

Licence: In copyright

Credit: Inorganic chemistry for advanced students / by Sir Henry Roscoe and Arthur Harden. Source: Wellcome Collection.

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    moving at a velocity of 200,000 kilometres a second. Owing to their high rate of motion these can penetrate thin layers of glass or metal, although they are stopped by thicker layers. The helium produced from radium has actually been collected (Ramsay and Soddy), and the rate at which it is produced has been determined and been found to be about 0.46 cubic millimetres of helium per gram, of radium per day. The helium in rocks and mineral springs has probably been formed in this way from radium. When the a particles fall on screens dusted with crystals of zinc sulphide they cause a series of flashes and it has been found that each such flash is caused by the impact of a single atom of helium. It is therefore possible in this way to see the effect produced by a single atom of matter and to count the number of atoms of helium given off in a certain time by a known weight of radium. The instrument devised to render this effect visible is called a spinthariscope (Greek, a spark). The number of helium atoms emitted can also be counted by an electrical method. The /3 particles are negatively charged, and very much lighter than the a particles and move with a much higher velocity, approaching that of light. They are able to penetrate considerable thicknesses of glass and metals. Their mass is about 201OQ part of that of a hydrogen atom and they seem to be identical with the particles given off from the cathode in the discharge of electricity through gases and known as the cathode rays. Similar particles are intimately concerned with the passage of electricity through conductors of all sorts, and they have therefore also received the name of electrons. The y-rays are still more penetrating in character than the /3-rays and appear to resemble the Rontgen-rays in their properties. 3. They evolve a gaseous substance known as the radium emanation, which can be removed by a mercury pump, liquefied and examined, but has only been obtained in quantities of about 0.1 cubic millimetre at a time. It is a colourless gas, probably belonging chemically to the argon series, and its atomic weight is about 220. Its spectrum has been observed and many of its physical properties ascertained. When cooled it forms a colourless liquid boiling at — 62°. It freezes at —71°, forming a solid which glows with great brilliancy, at first appearing steel blue, but at a lower tempera-