36 THE NEW KNOWLEDGE. 



because of the periodic law. Therefore we believe in the 

 periodic law. We believe that the weight of the atom 

 of the element fixes its properties and its position in a 

 great scheme of relationship. You will find many blank 

 spaces still in the table of the law ready for elements yet 

 in the womb of the future. So thoroughly does the chem- 

 ist believe in this law that he has not hesitated in several 

 instances to put certain " refractory" elements "in their 

 places." Thus, indium, beryllium and uranium would not 

 fit properly into their proper compartments in the table 

 on the basis of the old determinations of the atomic 

 weights. Renewed investigation, however, showed the er- 

 rors of these old determinations, and the new atomic 

 weights, accurately adjusted, allowed them to fall straight 

 into the positions to which they naturally belong in the 

 table, and which they hold to-day. 



One concluding and conclusive test of the validity of the 

 law was found in the discovery of the rare gases of the 

 atmosphere by Lord Rayleigh and Sir William Ramsay. 

 The history of their discovery is interesting. In 1893 Lord 

 Rayleigh undertook to determine the density of nitrogen with 

 all the accuracy of present-day science. To his astonish- 

 ment, he discovered that nitrogen from the air and nitrogen 

 from chemical compounds did not weigh the same. The dif- 

 ference was small but exasperatingly constant. Out of this 

 curious anomaly arose the discovery of a new and hitherto 

 unsuspected element of the air which had been weighed as 

 nitrogen and considered as nitrogen by all preceding chem- 

 ists. This new element was named argon and it constitutes 

 nearly one per cent, of the air we breathe. Subsequently 

 this " argon " was discovered to be itself impure, and 

 from it were isolated four other elements, helium, neon, 

 krypton and xenon. These five new elements are all 



