Further, most of the matter in the world is composed of a variety of elementary substances, limited in number. When more complex bodies are analyzed or broken-down, these elementary substances are always found. The number of those in Dalton’s day was unknown; but they had long been known as _elements_. Elements were, of course, composed of their own particular atoms; while all other substances were made-up of combinations of elements. THE ELEMENTS Dalton’s views ushered in a new era in chemistry. Prolonged researches were at once undertaken, in order to determine the precise atomic weights--investigations which are being carried on even today. The exact size, shape, texture, etc., of the atom was subject to endless investigation. The nature of chemical combinations (how two elements combine with one another) held the fascinated attention of chemists for a hundred years, and it is only within the past few years that a definite solution has been found, and this has only been rendered possible by the newer views of matter, entirely different from those maintained during the past century. During the hundred years which have elapsed since Dalton’s time, a number of new elements have been discovered, and there are reasons for supposing that there are some yet to discover. It is now believed, however, that there are 92 primary elements, of which Hydrogen has the lowest atomic weight, and Uranium the highest. Typical elements are: Oxygen, Iron, Fluorine, Silver, Sodium, Sulphur, Gold, Zinc, Copper, etc. A complete list may be found in any standard Chemistry. ATOMIC WEIGHTS When work was undertaken, to discover the exact atomic weights of these various elements, it was soon found that these could not be expressed in _exact_, whole numbers. Fractions or decimal numbers were nearly always found to exist. Thus, the atomic weight of Hydrogen was not exactly 1, but 1.008; copper was 63.57, etc. For long it was thought that these variations were due to errors of experiment, and renewed attempts were made to reach more accurate conclusions, in which these apparently annoying fractions were absent. But the most painstaking experimental work only served to confirm these results, and still later researches have shown us _why_ this is so. It would take us too far afield, however, to go into that question at present. The various elements were given symbols for the sake of brevity; some of these represented the first letters of the name of the element; some were the first letters of the Latin word for that element. Thus, Co = Cobalt, S = Sulphur, Ne = Neon, Bi = Bismuth. On the other hand, Fe = Iron (Latin, ferrum), etc. This served greatly to abbreviate chemical language, and at the same time simplified chemical formulæ and equations. VALENCY