486 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



within a month by the addition to the table of a series of 

 consecutive numbers (p. 457), and by the discovery of the 

 Law of Octaves as applied to these integers. 



In these early atomic numbers no space was left for 

 undiscovered elements and the correctness of the numbers 

 could only be checked by the vague indications of the Law 

 of Octaves. Newlands attempted to overcome this difficulty 

 by tabulating the ratios of the atomic weights to the atomic 

 numbers and showing that the ratios increased from 2-5 to 

 2 7 5 to 3 to 4 approximately (Periodic Law, p. 15). But it 

 was not until Mendeleeff's prediction of missing elements 

 had been justified by the discovery of gallium in 1875 

 that Newlands attempted a more open spacing of the 

 atomic numbers. Two tables were published in 1878 

 (Periodic Law, facing p. 32) to illustrate the new system of 

 atomic numbers. In the first the atomic weights were 

 divided by 2*3, so that Na= 10 ; the elements were arranged 

 in sixteen octaves, separate columns being assigned to 

 hydrogen, to the groups of transition elements, and at the 

 end of the table to the two elements thorium and uranium, 

 whilst two octaves were left vacant in the region now 

 occupied by the rare-earth elements. In this scheme of 

 atomic numbers 



the number in brackets being the atomic numbers, and the 

 numbers in italics the reducd atomic weights ; the reduced 

 atomic weights and the atomic numbers usually agreed within 

 a few units and there were forty vacant spaces. In the 

 second table the atomic numbers were divided by 2-37, so 

 that 0=15; hydrogen, and the octaves beginning with 

 sodium and lithium, were followed by nine columns of ten 

 elements, the transition elements being placed below the 

 octaves in the longer columns. In this scheme 



= 0-422, 



