14 C. E. FAWSITT. 



light of recent research these discontinuities are not so 

 numerous. It was for a long time a puzzle why so many 

 elements had a value for the atomic weight which was not 

 a whole number or even a multiple of 0'5. This is no 

 longer so striking in view of the fact that we must now 

 sometimes put several elements of different atomic weight 

 into the same place of the table. A large proportion of 

 the elements of low atomic number have atomic weights 

 which are whole numbers or very nearly whole numbers, 

 and this almost certainly not accidental. It has been 

 suggested that the mass of the atom of many of these 

 elements might be made up of the mass nuclei of hydrogen 

 and helium, but no definite conclusion in regard to this can 

 be stated yet. The striking difference in the chemical 

 properties that is noticed as we go from one vertical 

 column to another might have been looked upon at one 

 time as a discontinuity; indeed, Soddy said (6) a few years 

 ago that "The periodic law expresses a per saltum rather 

 than a gradual change in chemical properties;" but the 

 association of this difference, in some cases at any rate, 

 with the loss of an electron in the inner nucleus of the 

 atom, to some extent removes the surprise we might other- 

 wise have in examining the difference in properties in the 

 elements of two neighbouring columns. But one great 

 difficulty remains. The periodic table gives us a great 

 respect for the orderliness of Nature as we proceed from 

 hydrogen (No. I) to lanthanum (No. 57). It is, however, 

 not possible to place the elements Nos. 58 - 72 in any column 

 definitely; if we were determined to do so, we would be 

 forced to put a large number of these elements in one place, 

 on account of their similar valencies, which would also be 

 erroneous, as the chemical properties of the individuals of 

 the rare earth-group, while being very similar, are not 

 identical. After this great lapse in regularity, the elements 

 in the table may again be suitably placed from Nos. 73 to 



