ADDRESS BY PROFESSOR JOHN W. LANGLEY, VICE PRESIDENT, SECTION C. FELLOW MEMBERS OF THE CHEMICAL SECTION: LADIES AND GENTLEMEN: IN reviewing the history of each living being and of every intellectual conception, we are at once made aware of a law of growth the most general and fundamental possible, namely, that of development, or progression along what often seems to be a predetermined line whose constraining influence is so powerful that it is only by following it that the organism can escape destruction. Development, while it may be continuous, both for the individual. and for the race when broadly looked at over large intervals of time, is, on the other hand, a process which, in its details, is constantly interrupted both by alterations of direction and by arrests of action which may even go so far as to cause retrograde metamorphoses. A plant may readily grow unsymmetrically if shaded on one side; but that error of form will be largely corrected when it is again bathed with light which comes from all directions. This partial arrest may even arise from the plant itself, as when the excessive growth of the vine in forming new wood saps the energy which should go to the formation of fruit, and the grapes, which alone make the plant valuable to man, never reach that fullness and flavor which should recompense the toil of the husbandman. All of us here are constituent intellectual atoms in a great ideal organism called Chemistry. We know the long and honorable history of our science; we know, too, its wonderful progress in the past fifty years; we perceive how from the single stem of Alchemy it has thrown out branches in all directions, mineral, organic, analytical, synthetic, agricultural, physiological, biological chemistries; but has it furnished a corresponding number of great farreaching laws? Has it been equally prolific of grand hypotheses which have stood the test of time? Will you pardon me if I venture to apply the analogy of the plant, and to ask whether our development has been symmetrical, whether some struggling bud put forth in our youth has not been starved and shaded by the abundant leafage of our branches, and whether in the rapid accumulation of facts from that great diffused solution of them called Nature, while we may have greatly increased our quantities of chlorophyll and cellulose, we have equally gained in the fruit, whether we have been equally successful in elaborating well-rounded generalizations which fill the intellectual taste with a sense of delight, and which stand forth as the declared fruit of our toil. Such a bud our science put forth in its alchemical stage under the name of affinity. During the early part of the present century the idea received considerable expansion and showed, at one time, a vitality comparable with the condition of the doctrine of the conservation of energy prior to the year 1850. Having reached this stage the development of a theory of affinity seems to have been arrested and soon it is seen occupying a position of constantly decreasing interest to chemists. The proof of this statement is easily found by comparing such works as Daniel's Introduction to Chemical Philosophy, Thompson's History of Chemistry and Daubeny's Atomic Theory, published in 1830 and '31, or the works of Berzelius, with any recent manual of inorganic chemistry. In the older books the amount of space given to the treatment of chemical affinity is relatively large, while in the treatises of to-day it is in many cases hardly even mentioned. In the article Chemistry in the new Encyclopædia Britannica, covering 120 pages, there is not a single paragraph referred to the title affinity, and less than half a page devoted to it indirectly. In Watts' Dictionary of Chemistry, including the supplements, out of a total of 9665 pages, only 62 are devoted to affinity where it appears under the head of chemical action. In Wurtz's Dictionnaire de Chimie, the treatment of affinity under the several heads of chaleur, electro chimie, affinité, atomicité, etc., is relatively fuller, but still the proportion is quite small, and in that excellent manual Remsen's Theoretical Chemistry, the second edition of which was published last year, the word affinity does not even occur in the index. The causes of this almost complete abandonment of a word, and an hypothesis at one time considered of fundamental importance, can best be traced by reviewing briefly the history of that part of speculative chemistry which is related to the doctrine in question; a review which will show us that it is the word only which has become obsolete, the idea behind it is still active and of great importance. I will, therefore, venture to ask your attention to what I am only too well aware is but a sketch of the development of theories concerning the nature and fundamental cause, or causes, of chemical phenomena. I. The Conception of Affinity. The earliest appearance of the idea which has since been named chemical affinity is found in the writings of Hippocrates in the fifth century B. C., where the opinion is expressed that when two bodies unite to form a compound, a certain common principle must indwell in them, for it is laid down as a fundamental postulate that "like unites only with like,” hence the two bodies must possess some common principle, or have a bond of kinship between them.1 This conception prevailed with more or less clearness for several centuries, but it is not till the year 1698 that we find the word affinitas employed and defined. It first occurs in the writings of the alchemist Barchusen,2 and the conceptions of Hippocrates were still the ruling ones. Thus Barchusen explains the impossibility of completely isolating the four elements by saying that they have for each other a strong affinity which causes one to mingle with another, and which cause is derived from a principle common to them all. Boerhaave, the celebrated physician of Leyden, in his elements of chemistry, which appeared about 1732, was the first to extend the meaning of the term affinitas or Verwandtschaft, since he says, "The effort also of like substances to unite is due to the working of the same force;"3 and elsewhere in explaining the cause of solution, he says, "In this last case" (that of the action of aqua regia on gold), “why do not the particles of gold, which are nineteen times heavier than the particles of aqua regia, collect together in the bottom of the vessel? Do you not see clearly that there is between each particle of gold and each particle of aqua regia a force in virtue of which they seek each other out, unite and retain each other?"4 We also notice in Boerhaave's writings a tendency to regard combination as due to the attraction of opposite, rather than to the union of similar qualities; for he compares the action of an acid upon iron to a marriage, and says that the combination comes rather from love than hate. Two of Boerhaave's successors, St. F. Geoffroy and Torbern Bergman, appear to be the authors of a new conception which was subsequently known under the name of elective affinity. Geoffroy attempts to indicate the order of chemical actions, or, as we should now call it, the relative intensity of combining power, by arranging several bases in the order in which they displace each other. Thus one of his tables was the following: VITRIOLIC ACID.5 Sel alkali fixed. Sel alkali volatile. Earths. Iron. Copper. It was soon discovered, however, that an order of bases which might be correct for one acid would be incorrect for another, and that a given substance would take different positions in the two. The following, which is a portion of one of Bergman's lists, published in 1783, will show the fact.6 The reversal of the order of attraction was explained by assuming the existence of preferences or special attractions between. acids and certain bases and was known under the name elective affinity, a term which has remained in chemical literature till quite recent times, and, indeed, was very generally used within the recollection of most of us here present. The chemist Glauber, 1689, was one of the first to recognize this fact of differential attractions. He teaches that "potash, lime and zinc oxide, with application of heat, drive out ammonia from sal ammoniac because the zinc, as also potash and lime, is of such a nature that it has a great community of interest with all acids, loves them and is also loved by them; accordingly when warmed, the acid of the salt (muriatic) attaches itself to it, combines with it so that the sal volatile is set free and is distilled to a subtle spirit." The next advance in the direction of precision was made by Wenzel, who, in a work entitled Lehre von den Verwandschaften published in Dresden in 1777, showed that when two neutral salts act upon each other by double decomposition, the new salts formed are also neutral and thus prove chemical unions to be governed by some general law which determines how much of one acid must be taken to displace another. Although Wenzel's work attracted but little attention at the time, we can now see on looking back that it marked a very important discovery, for he must be regarded as the first man who apprehended with any distinctness that fundamental law of chemistry, definiteness of action, which was subsequently enunciated and is familiar to us to-day under the name of the "law of definite proportions." The final result of Wenzel's discovery was the establishment of the law of equivalent proportions through the labors of Richter, Thompson, Wollaston, Berzelius and others, and from equivalent proportions sprang the Daltonian hypothesis of atoms which has developed into the all but universally accepted atomic theory of the present day. The atomic theory, however, is not necessarily coterminous with hypotheses about affinity, and indeed in many respects it is independent of them; the development of its history is therefore foreign to the purposes of this paper, but if we turn back to the period which immediately follows Wenzel's discovery, which was that of the re-birth of the atomistic theory of the Greeks under Dalton's parentage, we see that it emerged from opposing views about the nature of affinity, and at this point, therefore, the two speculations have a common history. The opening of the present century witnessed an active controversy between the advocates of the new, or equivalent and atomistic school, and the partisans of the older philosophy. Prominent among the latter stands |