This pioneer work of Newlands rendered possible the Periodic Law, as finally formulated and worked out in detail by Mendeleeff. Briefly, the Law states that “the properties of an element are a periodic function of its atomic weight.”
This is merely another way of saying that if you know the atomic weight of an element, you also know its properties, since these are fixed or invariable. Mendeleeff arranged the elements in various “Groups,” according to their atomic weights, and it was found that the properties of the elements periodically recur as the weights of the atoms rise. There were certain empty spaces in Mendeleeff’s Table, waiting for new elements which should fit into these empty spaces, if discovered. At the time they had not been discovered; but several of them have been since, and it is a remarkable fact that they invariably fit into his table exhibiting all the properties which they should theoretically exhibit, and might have been predicted to, years before. This is one of the surest confirmations of the accuracy of Mendeleeff’s general Law, and is one of the finest generalizations ever made in science.
The conclusion which we may draw from this Law is that there is a definite relationship between the chemical elements. How or why this relationship existed was not known at the time, and only became clear half a century later, when the newer discoveries concerning the ultimate constitution of matter rendered this clear.
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! Had every 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!
ANALYSIS AND SYNTHESIS
Compounds may be broken up into their constituents, during the process of analysis, or they may be made to combine one with another, in synthesis. All the resources of modern science have been brought to bear, in efforts to effect these various alterations or changes. Great heat, extreme cold, chemical reägents, enormous pressures, high vacua, electrical currents and sparks, bombardment with radio-activity, etc.—all have been employed in these chemical investigations. Suitable laboratories have been constructed, encasing immense boilers, huge refrigeration machines, electrical contrivances of all kinds, etc. What tremendous strides have been made in this field during the past century—from the simple glass retorts, flasks and apparatus of a century ago! But this only shows us how tremendous would be our progress could men but learn to work together, in harmony, welded together by a common interest,—instead of butchering one another, or wasting their precious lives and energies in scandals and political intrigues!
But let us return to earth again—to matter—the subject of chemistry!