But the investigation of Liebig and Wöhler served to give precision to the conception. It thereby exercised a profound influence on the development of organic chemistry by demonstrating, in effect, that this branch of the science might be regarded as the chemistry of the compound radicals, in contradistinction to inorganic chemistry—the chemistry of the simple radicals. Additional support for this view was afforded by the remarkable research by Bunsen on the so-called _alkarsin_, the “fuming liquor of Cadet”—an evil-smelling substance long known as being formed when an acetate is heated with arsenious oxide. Bunsen showed that this liquid contained a compound radical having arsenic as a constituent; and he prepared a series of derivatives, all of which might be formulated as combinations of this radical, which he termed _cacodyl_. The study of the electrolytic decomposition of the acetates by Kolbe and the discovery of _zinc-ethyl_ by Frankland afforded powerful support to the doctrine of combined radicals. Although there can be no doubt that this doctrine greatly stimulated the pursuit of organic chemistry, it was gradually perceived that to regard inorganic and organic chemistry as the chemistry respectively of the simple and of the compound radicals was an imperfect and misleading conception of the true relations of the two main divisions of the science. Facts showed that the properties of a substance depend more on the arrangement of its atoms than on their nature. The doctrine of compound radicals was implicitly an attempt to extend the dualistic conceptions of Berzelius to the facts of organic chemistry; and as such it was welcomed by the great Swedish chemist. But dualism was found to have its limitations, even in inorganic chemistry; and these were still more apparent when it was sought to apply it in the other main branch of the science. Attempts were therefore made—notably by the French chemists Laurent, Dumas, and Gerhardt—to formulate organic substances by methods in which the electro-chemical and dualistic conceptions of Berzelius and his followers had no part. How these attempts developed, and how they subsequently grew into the organic chemistry of to-day, will be shown in the second part of this work. It will be convenient also to delay any account of the personal history of the creators of the science of organic chemistry—Liebig, Wöhler, Dumas—until we are in a position to give a fuller statement of their labours, and of the results which flowed from them. Although the foundations of organic chemistry may be said to have been laid during the closing years of the first half of the nineteenth century, the superstructure was not erected until the second half. CHAPTER XII THE RISE OF PHYSICAL CHEMISTRY