* The elements are naturally classified in several families or groups, as the group of the alkaline elements, the halogen group, and the like. They are roughly divided into two great classes, the metals, as sodium, calcium, etc., which form basic compounds, and the nonmetals or metalloids, as oxygen, sulphur, chlorine, which form acid compounds; but the distinction is only relative, and some, as arsenic, tin, aluminium, etc., form both acid and basic compounds. The essential fact regarding every element is its relative atomic weight or equivalent. When the elements are tabulated in the order of their ascending atomic weights, the arrangement constitutes the series of the Periodic law of Mendelejeff. See Periodic law, under Periodic. This Periodic law enables us to predict the qualities of unknown elements. The number of elements known is about seventy-five, but the gaps in the Periodic law indicate the possibility of many more. Many of the elements with which we are familiar, as hydrogen, carbon, iron, gold, etc., have been recognized, by means of spectrum analysis, in the sun and the fixed stars. From certain evidence (as that afforded by the Periodic law, spectrum analysis, etc.) it appears that the chemical elements probably may not be simple bodies, but only very stable compounds of some simpler body or bodies. In formulas, the elements are designated by abbreviations of their names in Latin or New Latin.

Several other elements have been announced, as holmium, vesbium, austrium, etc., but their properties, and in some cases their existence, have not yet been definitely established.

The simplicity which is so large an element in a noble nature was laughed to scorn. Jowett (Thucyd.).