All of these statements have been verified, and the immediate acceptance of Alendekieff's views was facilitated especially by the sensational dis covery of a number of elements whose properties agreed aceurately with those predicted by Alen deleett. Mils gallium, germanium, and scan dium had been completely described with respect to their own properties and those of their com pounds before they were actually discovered. Success has also attended the attempts to correct atomic weights in several cases where the ele ments appeared misplaced in the original tables and were assigned to positions more in accordance with their properties, but necessitating the assign ment of new atomic weights. (See ATOM IC Wmoturs.) The weakest point of the table lies in the position of tellurium. which should fall in the sixth group, but is found to have a higher atomic weight than iodine, which undoubtedly be longs to the same series in the seventh group.
Efforts to explain this discrepancy have been so far unavailing. There are also a number of ele ments derived from the so-called rare earths whose place in the system is not readily assign able. In the latter case, however, it may be said, as well as in that of the atmospheric gases, argon, helium, neon, and krypton, that their properties and atomic weights are not so well established as to cast doubt upon the theory through their fail ure to coincide with it. One interesting result of the theory is that of limiting the probable num ber of chemical elements to about 120, since the actual number of blank spaces is limited, and since it is extremely unlikely that any elements remain to be discovered with an atomic weight less than that of hydrogen or greater than that of Among the physical properties which appear as periodic functions of the atomic weight may be mentioned the densities of the uncombined elements and of their oxides, fusibility, atomic volume, crystalline structure of the compounds, coefficient of expansion, refractive index, eon duetivity for heat and electricity, color, and velocity as ions.
As all indication of some purely chemical peri odieities the following conspectus has been ar ranged, in which the elements are indicated by their positions in the above table, and are gen erally enumerated in such order that the one which shows the property in the most marked degree has precedence. The maximum valency of the elements toward oxygen is indicated through out by the Roman numeral of each group, omit ting the 'peroxides.' in which the oxygen appears to be linked in a different manner.
,Nlaximum valency toward hydrogen in stable volatile compounds: Consult; Newlands, On the Discovery of the riodie Lair and on Relations Among the Atomic Wriahts (London, 1Ss4) ; Utah, bus periodische Ues,t: der .itomgewirhtc unit das man rliehe Sus i( in der Elemrnte (Frankfurt a. 0., 1884) ; /his periodische am( des natiirliehc nt der El, went(' (Laibadi. 1897) ; Principles of Chemistry," in A Li brary of Universal Literature ( New York. 1901) ; Venable, .1 Bibliography of the Periodic Law Easton, Pa., 189G).