ORGANIC CHEMISTRY. When the general prin ciples of chemistry were established, and the atomic had lent, to the science a keen power of penetration, 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 chemist, almost exclusively during a greater part of the Nine teenth Century, and the result of that inquiry leas been not only a vast store of empirieal knowledge of organic compounds. hut also a set of general prineipleQ, that have strengthened the theoretical basis of the science, and have led to some of the great industrial achievements of modern times.
Early in the Nineteenth Century it was uni versall• believed that organic substances could not be produced without the agency of the 'force of life.' Whether there is such a distinct 'force,' and what its relations may be to the measurable berms of energy, we do not know as yet., But we dee know that organic compounds can also be produced by chemical agencies alone, without the intervention eef anything else. For chemists have actually suec•eded in building up from their elements many theensands of that occur ready formed only in the of animals and plants. The first of such compounds reproduced in the laboratory was urea, which Wahler made artificially in The old be lief, however, lingered, some chemists contend that urea could not be looked upon as a true organic compound. But when Kolbe synthesized acetic acid in V445, and when other indisputably organic compounds were made from their ele ments, then all agreed that there was no essen tial difference between 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 ea rbon compounds that are not known to occur 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. Berzelins was led to this problem by his electro-chemi•al theory. But in the twenties facts became known which made its study an imperative necessity also from a purely prac deal standpoint. Not small was the surprise of chemists when Gay-Lussac and Liebig found. in 1823, that silver fulminate had precisely the same composition as silver cyanate. Two years Liter. Faraday discovered a volatile liquid hydro carbon that had precisely the same composition as ethylene gas. Berzelius first thought it un wise to abolish, 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. lent also on its constitution—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 1832 Liebig and Milder made an important discovery: A series of compounds allied to ben zoi• 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, henzahlehyde, benzamide, and hen zoyl chloride. contained that radicle in eommon, as if it were a single atom of some element. The discovery of henzoyl was followed by Liebig's. discovery of ethyl, 11 radicle common to ordinary alcohol and ether, and by Bunsen's discovery of cacodyl, which is possessed in common by several compounds of arsenic. The discovery of radicles was obviously the first step toward a knowledge of the constitution of compounds. But almost from the beginning the idea of radieles became associated with certain other ideas that could not be maintained in the light of more knowl edge. Berzelius subdivided organic radicles. like the (dements, into electro-positive and electro negative. On the other hand, it was generally expected that radicles would eventually be iso lated and thus constitute a series of simple com pounds whose molecules would bear the same re lation to the substances of organic chemistry as the atoms of the elements bear to the com pounds of inorganic chemistry. But When the
electro-chemieal theory was overthrown, while attempts to isolate radicles remained fruitless, the opinion began to spread that the theory of radicles had made of organic ehemistry a science of imaginary substances, and, hence. the sooner the theory was abolished the better for the science. But how, then, were Organic compounds to lie correlated? A solution of this problem was suggested by Dumas in 1.'7;39. Continuing his reset rehes on the substitution of different elements for one another in organic compounds, Dumas found that in acetic acid hydrogen could lie exchanged for ehlorine. and that the resulting compound triehlor-acetie acid) was very much like acetic acid itself. ;simila• facts had already Keen observed, since 183-1, by himself as well as by Laurent. It now occurred to Dumas that in correlating their substances ehemists could lie guided solely by the phenomena of substitution. Aeetie acid and its chlorine-sithstitiltion product obviously belong to the same 'type,' and similar relations exist between other substances as well. If. therefore, the phenomena of substitution were investigated in connection with organic com pounds in general. the result would be a group ing of compounds free from all hypothesis, but based on and exhibiting, clearly their natural relationship. Such were. in num, Dumas's views, on the basis of which the celebrated 'theory of types' was gradually built up in course of the fourth and fifth decades. The most important contributions to the theory were made by Ger hardt, Wurtz. and Williamson. Ger hardt realized that Dunias's ideas were worthy of being developed, lint he also realized that this •onld not lie done without the aid of the idea of radicles. No objection could be raised against the latter idea. once it were freed from all un npvps:a ry associations, especially from the belief that radicles were unalterable substances capable of independent existence. To say that ben voyl chloride, benzoic acid. and benzamide. contain in common the b•nzoyl radiele—i.e. the group of atoms was only to express what was evident from their formulas. On the other hand. the recognition of radieles must obviously lead to the discovery of the relationship of compounds, and thus, to gether with the phenomena of substitution, guide in grouping compounds in accordance with the iiLa of types. In IS-19 Wurtz and 'Hofmann discovered a series of compounds that bore an unmistakable resemblance to ordinary ammonia. and could lie considered as ammonia in which one or more hydrogen atoms were replaced by radicles. They proposed to group them together as belonging to the 'ammonia type.' in 1850 Williamson showed that alcohols, ethers, and acids could be referred to the 'water type.' Or dinary alcohol, for instamp, whose formula is could be considered as water, 11P, in which one hydrogen atom has been replaced by the ethyl radicle, Ordinary ether, could be considered as water, in which two hydrogen atoms have been replaced by two ethyl radicles. ether being tinis Acetic acid. emild be considered as water, 11,0, in which one hydrogen atom has been replaced by the radicle Now, ether. was obtained from aleohol. by the use of dehydrating agents. Williamson therefore held, by analogy, that it ought to he possible to hailstorm acetic acid. 0.110, into a com pound. ( When. in 1852, Frankland actually succeeded in effecting this transforma tion by the use of dehydrating agents, the use fulness of the type theory was demonstrated. For nothing is more striking proof of the value of a theory than its capacity for revealing lin known facts. To the types ammo»ia and water Gerhardt added the types hydrogrn and hydro chlo•ic acid, and for a time it seemed that all organic compounds could he grouped under these four simple types. It was soon found necessary, however. to introduce the ideas of 'condensed types,' like the condensed water type, (IUD,. `mixed types: and the type marsh yas, CH,. In eourse of the fifties the type theory tints gradu ally became less and less simple. and, hence, less and less valuable for the purpose of organic eompoinids.