Page:The New International Encyclopædia 1st ed. v. 04.djvu/653

* CHEMISTRY. 571 CHEMISTRY. ponent of acids, and this view was further strenjrthened by Graham's and Liebig's classical studies of the so-called ]iol_vliasio acids. But so profound was I?crzelius"s belief in dualism, and so great «as his authority, that the electro- chemical theory still continued to stand, and the conclusions just pointed out were not generally accepted for some years. The final blow to dual- ism came fiom the young or-ranic chemistry, in which the electric theor.v had been applied as generally as in the inorfjanie branch of the science, .bout the middle of the thirties Lau- rent and Dumas made a series of important dis- coveries showing that chlorine and other ele- ments could be substituted for the hydrogen of or- ganic compounds, and that the nature of the lat- ter was thereby affected verv little. But if part of the molecule of a compound can combine with either of such electrically diti'erent atoms as those of hydrogen and of chlorine, then there is 110 reason for believing that that part is essen- tially either electro-positive or electro-negative, and hence there is no reason for believing that everv compound is made up of two electrically opposite parts. The more evidence to this effect was brotight forward, the more bitterly old Ber- zelius adhered to the electro-chemical theory. But finall.v it became evident to all that, as Liebig wrote, "the wheel of time cannot stand still," and ••Berzelius is fighting for a lost tause:" and thus, toward the end of the thirties, electro-chemical dualism was overthro«Ti. As a result of their struggle against dualism, chem- ists then fell into the opposite extreme, and adopted a purely imitary view of chemical com- bination. The molecule of a compound was conceived to be a composite unit somewhat like the solar s.vstem, in which the planets are held together by mutual attraction, but which does not by any means consist of two essentially dif- ferent parts, endowed with two opposite forms of energy. Such imitary views of combination are still prevalent in chemistry to-day. But "the wheel of time cannot stand still," and re- cent years have forced upon us theories which make us feel that extreme unitarism is just as inadequate as extreme dualism. Tlie elements certainly ditTer in their electrical properties, and chemists have even succeeded now in expressing those differences mathematically. Electricity, ■while not identical with the energy- that causes the mutual attraction of atoms, is yet certainly one of the factors determining that attraction. At present, however, it is impossible to tell what compromise between chemical unitarism and electrochemical dualism will ultimately be adopted. Orgaxtc Chemistry, When the general prin- ciples of chemistry were established, and the atomic hypothesis had lent to the science a keen power of lunetration. it became possible to ap- proach the world of organic matter with the hope of shedding some light upon its mystery. Since then organic research occupied chemists almost exclusively during a gieater part of the Nine- teenth Century, and the result of that inquiry lias been not only a vast store of empirical knowledge of organic compounds, but also a set of general principles that have strengthened the theoretical basis of the science, and have led to some of the great industrial achievements of modem times. Early in the Nineteenth Century it was vini- Vnl.. IV.— 37. vcrsally believed that organic substances could not he produced without the agenc.v of the 'force of life.' Whether there is such a distinct 'force.' and what its relations may be to the measurable forms of energy, we do not know as yet.. But we do know that organic compounds can also lie produced by chemical agencies alone, without the inter'ention of anvthing else. For chemists have actually succeeded in building up from their elements many thousands of compounds that occur ready foriued only in the organisms of animals and plants. The first of such compounds r<>produced in the laboratory was urea, which Wiihier made artificially in "l8'28. The old be- lief, however, lingered, some chemists contend- ing that urea could not be looked upon as a true organic compound. But when Ivolbe synthesized acetic acid in 184.5, and when other indisputably organic compounds were made from their ele- ments, then all agreed that there was no essen- tial difference Ix-tween organic and inorganic compounds, and that the former were nothing but the compounds of carbon. At present many dyestuffs, drugs, and perfumes, which could once be obtained only from plants, are made artificial- ly on a large scale, and so are many valuable carbon compounds that are not known to ix'cur ready formed at all. While the belief in an indispensable force of life thus delayed for a time the progress of chemical synthesis, chemists early directed their attention to the problem of molecular constitu- tion. Berzelius was led to this problem by his electro-chemical theory. But in the twenties facts became known which made its study an imperative necessit.v also from a purely prac- tical standpoint. Not small wa-s the surprise of chemists when Gay-Lussae and Liebig found, in 1823, that silver fulminate had precisely the same composition as silver c.vanate. Two years later, Faraday discovered a volatile liquid hydro- carbon that had precisely the same composition as ethylene gas. Berzelius first thought it un- wise to alwlish, on the evidence of a few facts, what had seemed an axiom — viz. that two dif- ferent compounds cannot possibly have the same composition. But when he discovered that race- mic and tartaric acids, too, had the same com- position, he realized that the character of a sub- stance must depend not only on its composition. but also on its coiixtittitirm — i.e. not only on the kind and number, but also on the arrangement of the atoms in its molecule. Thus was born that great problem of modern chemistry — to deter- mine the constitution of substances from the standpoint of the atomic hypothesis. In 183'2 Liebig and Wiihler made an important discoveri': A series of compounds allied to ben- zoic acid were transformed by them into one an- other, and through all the transformations a group of atoms (made up of carbon, hydrogen. and oxygen), which they named 'the benzoyl radicle,' remained unchanged: the molecules of benzoic acid, benzaldehyde. bcnzamide, and ben- zoyl chloride, contained that radicle in comnmn, as if it were a single atom of some element. The discovery of benzoyl was followed by Liebig's discovery of ethjd, a radicle common to ordinary alcohol and ether, and by Bunscn's discovery of cacodyl, which is possessed in common by several compotmds of arsenic. The discovery of radicles was obviously the first step toward a knowledge of the constitution of compounds. But almost