these facts, he constructed formulæ for all compounds, which formulæ were made up of two parts, or radicles. The idea of compound radicles was thus closely associated with the dualistic theories of the Berzelian school. The new school, led by Dumas, finding dualism insufficient to explain many weighty facts, naturally waged war against the fundamental conception of compound radicles, but they were soon obliged to accept the essential truth of the theory which they at first opposed. Liebig and Wöhler's research on oil of bitter almonds led to the discovery of a number of compounds, exhibiting many general analogies, which could best be explained by supposing the existence in each of a compound radicle, or group of atoms. When it became necessary once more to adopt the idea of compound radicles, the theory of substitution was found to be strengthened, not weakened, thereby. Many reactions were made clear by supposing that an element might be substituted by a group of elementary atoms, by a compound radicle. But in adopting the idea of compound radicles the substitutionist yet maintained that the chemical compound was a distinct whole, made up of parts he admitted, but, nevertheless, having these parts so modified and merged in one another that the resultant acted as an homogeneous compound. Thus, when the new school likened the ethers to the metallic oxides, they did not mean to assert that the molecule of ether was composed of two parts, ethyl and oxygen, held together by electric bonds, and ready to part company without difficulty; nor, in asserting that ether was one substance, and not a dualistic system, did they deny the existence of a structure within the molecule of ether. They admitted the existence of a closer relationship between the atoms of carbon and hydrogen constituting the group ethyl than between these atoms and those of oxygen, and they generalized the reactions and analogies of ether, by saying that it might be regarded as sodium oxide in which both sodium-atoms had been substituted by two compound atoms of ethyl. Berzelius had himself likened the ethers to oxide of potassium, and by doing this the great apostle of dualism had paved the way for the advance of the unitary theory.
That portion of the dualistic doctrine which was embodied in the theory of compound radicles was adopted by the unitary schools, but adopted in a modified form; the effects of this modification were not long in making themselves felt.
Berzelius, in his later works, had been ready to give a dualistic formula to any compound without stopping to inquire into the facts known about that compound; he had tended to forsake the only true scientific method, and to substitute the vagaries of his fancy for the facts of nature. The new school averred that "compound radicle" was an expression generalizing a class of facts; that the reactions of bodies were most simply explained by supposing that when acted on by chemical force the little parts of these bodies behaved as having a definite structure; and that therefore the formula of a given body
