CHEMICAL AFFINITY, the force or tendency which causes two or more dissimilar substances to combine in definite proportions to form a new substance, whose properties are distinct from those of any of the constituents. The word "affinity° was originally employed in this sense because it was believed that a kind of relationship exists between substances that are capable of combining with one another. No such idea as this is entertained in modern times, and it might even be said that the tend ency toward combination is (in general) stronger, in proportion to the dissimilarity, or lack of obvious relationship, between the sub stances combining. In the time of Aristotle the constituent particles of bodies were con ceived to be endowed with qualities somewhat akin to love and hate. After the advent of Galileo, these notions were exchanged for equally erroneous but more mechanical ones, and the ultimate, particles were represented, in thought, as provided with hooks and other similar devices, by means of which their corn binations were conceived to be effected. Later,
when the law of universal gravitation was pro pounded by Newton, the force impelling the atoms toward one another, and holding them in their combinations, was naturally enough pic tured as a special form, or manifestation, of gravitative action. This latter view may pos sibly be true, but if so we must modify our present views with regard to gravitation some what, and assume that it follows different laws, when acting at molecular distances, from what it does when acting at distances that are appre ciable to the senses. The modern tendency ap pears to be rather in favor of viewing chemical affinity as an electrical manifestation, though this conception has not yet been developed in a wholly definite and satisfying form. (See