Page:Popular Science Monthly Volume 36.djvu/692

674 Any common event, then, which may be selected by way of illustration, will furnish two elements open to scientific study—matter and motion. The distinction between the two is more convenient than essential, for we are unacquainted with matter devoid of motion, and the idea of motion divorced from matter is similarly unthinkable. However, the distinction is convenient, so that it will be well to follow it. The study of the analysis and synthesis of matter is the field of chemistry. The study of those varied motions which give to matter its apparent properties belongs to the domain of physics. The two sciences are commonly made the objects of separate study. It would be more true to nature to consider chemistry simply as a branch or subdivision of physics, for it is impossible to make any change in the constitution of matter without at the same time disturbing the physical equilibrium. Heat is either given out during the reaction or it is taken in. If it be chemical combination, heat is commonly disengaged; if a chemical disunion, heat is commonly involved. So general is the truth of this statement that we are able to predict what will occur chemically if the physical conditions are known. If there be two or more reactions possible, that one will take place which will liberate the greatest amount of heat. It is, indeed, the distinctive character of the so-called New Chemistry that it takes cognizance of the physical reaction which invariably accompanies the chemical. If the labors of Crookes, Roscoe, Hunt, and other eminent contemporary chemists count for anything, it is from such joint study as this that the best secrets of chemistry are to be evolved. With the view of lessening difficulties, this necessary interdependence between the chemical and physical is frequently omitted in presenting the science to young students; but the practice of teaching errors or half-truths, in order that the truth itself may afterward be apprehended, has as little excuse in science as it has in religion, for generally it is the error which proves obdurate, and the subsequent truth has no chance whatever. It robs the science, moreover, of an element of vitality which is one of its chief attractions.

In selecting our illustrations of chemical action, the more commonplace the event the better. The affairs of every-day life present such excellent objects for study that it would be as unnecessary as it would be uselessly distracting to go in search of the unusual, until the fundamental principles have been learned from a study of that which is familiar. That coal will burn, that milk will sour, that iron will rust, that cider will turn into vinegar, and that wood will decay, are all well-known facts of every-day life. But they are also facts of chemistry, for they involve a change in the composition of matter. It needs no scientist to perceive that the original coal, milk, iron, cider, and wood have