MENDEL^EFF 131 



elements the great Russian chemist gave the names, 

 ekaboron, ekaaluminium, and ekasilicon. In 1875 Bois- 

 baudran discovered gallium ; in 1879 Nilson found scan- 

 dium ; and in 1886 Winkler isolated germanium: 

 elements which exactly filled the vacant places or gaps 

 in Mendele"efFs series. Even their properties were similar 

 to those which had been foretold. The greatness of the 

 periodic law enables the chemist to predict what elements 

 will be discovered in the future, and what their chief 

 properties will be, as well as to systematize the varying 

 properties of the elements already known. 



The periodic law may be enunciated as follows : " If 

 the elements are arranged in the order of the numerical 

 value of their atomic weights, their properties, physical 

 and chemical, vary in recurrent or periodic manner." 

 And while doing this, " the periodic law keeps before us 

 the necessity of from time to time modifying our scheme 

 of classification : it reminds us that a typical classification 

 is of necessity temporary, but that just by reason of its 

 elasticity it is suited to the present needs of the chemistry 

 of solid and liquid substances." 



The work of the Russian savant on the periodic law 

 has been severely criticized ; but what great discovery 

 has not had fault-finders ? " They wholly mistake the 

 nature of criticism who think its business is principally 

 to find fault" (Dryden). The law deals with atomic 

 volumes, atomic weights, specific gravities, melting-points, 



