. The Becquerel rays and the properties of radium . ist of the elements in theorder of their atomic weights. Let us also tabulatethe value of some other measurable (quality of theelement such as the melting point, the boiling point,or the refraction equivalent. We shall then find that the properties of theelement do not increase regularly with the atomicweight, but they show a regular fluctuation. Everyeighth shows a return to the properties of the first. The best and clearest example of this is found,not in the properties already mentioned, but in theatomic volume of the element. The late Pro
. The Becquerel rays and the properties of radium . ist of the elements in theorder of their atomic weights. Let us also tabulatethe value of some other measurable (quality of theelement such as the melting point, the boiling point,or the refraction equivalent. We shall then find that the properties of theelement do not increase regularly with the atomicweight, but they show a regular fluctuation. Everyeighth shows a return to the properties of the first. The best and clearest example of this is found,not in the properties already mentioned, but in theatomic volume of the element. The late Professor PEODUCTS OF RADIO-ACTIVE CHANGE 163 Lothar Meyer of Tubingen was the first to drawattention to the striking periodicity of this atomic volume of an element is defined as thequotient of the atomic weight by the density. If wetake quantities of the different elements in the solidstate, proportional to their atomic weights, then itis evident that these quantities will each contain anequal number of atoms. Thus the volumes of these. O 20 HI 60 aO 100 )20 l-W 160 Atomxa Weights Fia. 2G.—Mnycrs curve, Rhowing tlepcndeucP of atomic volumes on atomic distances represent atomic weiglits; vertical ones atomic element is denoted by its chemical symbol. The atomic volume alternatelyincreases and diminishes as the atomic weight increases. The elements of very highatomic weight are not included, for tlicre are so few of them that the further courseof the curve is not clearly indicated. quantities are in the same ratio as the volumesoccupied by their respective atoms. The volume isfound by dividing the mass by the density. The quotients of the atomic weights by the re-spective densities are in the same ratio as thevolumes of their atoms, though, of course, not equal tothem. We cannot determine the volume of an atom 164 THE BECQUEREL RAYS absolutely by considerations of this kind. But wecan compare the volume of one atom with that ofanoth
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