Page:Popular Science Monthly Volume 82.djvu/587

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HEN we consider the marked resemblances and striking interrelations of the elements as expressed by the Periodic System, the conviction grows more and more strongly upon us that this system is the external expression of a fundamental process in nature, to which are due the general properties, as well as the individual characteristics, of the elements. On the present occasion I shall endeavor to point out that between the Periodic classification and the ordinary zoological classification, such analogies exist as tend to indicate an identity in fundamental principle. We shall then consider some of the phenomena which are at the foundation of the law of organic evolution, and here, too, we shall find among the elements conditions exactly corresponding.

Before proceeding farther, however, it is of interest to note the similarities which exist between a family of the elements and a homologous series of organic compounds. For the purpose of this comparison it is most useful to select the homologous series of fatty acids, $$C_{n}H_{2n+1}COOH$$. If we should arrange the normal acids of this series in order of molecular weight, we should find that between such a series and a family of the elements there exist certain close analogies, which are tabulated below in parallel columns.