EARLIER DISCOVERIES
Mendeleeff’s Law could not have been formulated had not an immense amount of research work preceded it, and a number of new elements been discovered. Such was, however, the case. Immediately following the great work of Lavoisier, a host of brilliant chemists appeared, and rapid and important advances were made in consequence. Cadmium was discovered by Stromeyer in 1817; lithium in the same year by Arfvedson. Silicon was isolated in 1810 by Berzelius. In 1827, Wohler isolated aluminum; and the same scientist also isolated beryllium the following year. Bromine was discovered by Balard in 1826; iodine, in 1811, by Courtois. Tellurium had been discovered by Muller von Reichenstein in 1782; Berzelius discovered an element closely analogous to it—selenium—in 1817. Elements continued to be added to the list—and then no more! Hadevery element been discovered? Some were inclined to think so. With the discovery of Radium, by the Curies, however, another whole list of elements was brought to light—all of which have been added to the Table of the Periodic Law.
Meanwhile, further discoveries of the curious properties of matter were being made. For example, it had been noticed that at least three distinct varieties of sulphur existed: (1) A pale yellow, brittle solid; (2) translucent needles; and (3) soft and rubber-like sulphur. These were all different physical varieties of one and the same substance—nevertheless they are all sulphur! This element, then, can assume more than one form, and because of this, the term “allotropic” has been applied, to signify the varieties of appearance which the same substance can be made to assume. A good example of this afforded by charcoal, graphite (or black-lead) and diamond,—which would hardly be suspected of being all the same substance; and yet they are!