Page:Biographies of Scientific Men.djvu/173

 elements the great Russian chemist gave the names, ekaboron, ekaaluminium, and ekasilicon. In 1875 Boisbaudran discovered gallium; in 1879 Nilson found scandium; and in 1886 Winkler isolated germanium: elements which exactly filled the vacant places or gaps in Mendeléeff's 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,