efforts to determine its constitution; but, finally, that prince of experimenters, Baeyer, of Munich, succeeded, and indigo is to-day manufactured from inert matter; and, though this manufactured article can not yet successfully compete with that obtained from the plant, it is, in my opinion, simply a question of time when the occupation of the plant will be gone.
The subject of the constitution or structure of chemical compounds at present receives more attention from working chemists than any other, and this has been the case ever since chemistry came to be a science. Great progress has been made, particularly within the past twenty or thirty years. In this field, as in that of the elements, to which I have already referred, wonderful predictions have been made and verified. Let me here quote a passage from an address by that eminent physiologist and philosopher Emil Du Bois-Reymond. He says: "I know of no more astonishing production of the human mind than structural chemistry. To develop, from that which appears to the five senses as quality and transformation of matter, such a doctrine as that of the relations between the hydrocarbons, could scarcely have been easier than to develop the mechanics of the planetary system from the motion of luminous points; and Strecker's prediction of the synthesis of creatine, which was afterward verified by Volhard, although in a less exalted sphere, was in fact no smaller achievement than the discovery of Neptune."
Of late, attempts have been made to go still further into the subject of structure, and to get some clew as to what we may call the actual shape of the minutest particles of which all forms of matter are believed to be made up. According to the prevailing theory, every kind of matter is made up of certain minute particles called molecules, and these molecules are conceived to be made up of still smaller particles called atoms. This theory is not merely a wild suggestion of dreamers, but it is forced upon us after a profound study of an immense number of facts. It is found that the facts can be explained only on this assumption. In chemical compounds it is believed that the atoms of elements are united with one another to form the molecules, and that the compounds are made up of these molecules, which are moving around freely in the case of a gas, less so in a liquid, and held together in solids. Now, the problem of the chemist is to determine how the atoms are arranged in the molecule—or to determine what connections exist between the atoms, without reference to the actual arrangement in space. When we consider that the atoms and molecules are almost infinitely small—so small, indeed, that we are told that the smallest particle of matter visible with the help of a good microscope must contain from sixty to one hundred millions of molecules—it does seem in the highest degree presump-
