always occur together in meteorites, and are the only magnetic metals. It is not impossible that, as chemical processes are made more accurate, future operators will find these three metals have a common basis, differently modified in the different cases. Similar close resemblances are found between other metals. We know that while our analytical methods have been greatly improved, yet much more labor is required to make them what they should be. Many of our separations are imperfect, and some substances cannot be separated from one another with our present means. The chemist engaged in research is groping his way in the dark, and is constantly liable to arrive at erroneous conclusions. Many of the best chemists have been led into error. Wohler mistook a compound of boron and nitrogen for boron itself. Rose thought he had discovered in certain rare minerals the acid oxides of two new metals, niobium and pelopium, and it was only after years of labor he found that his pelopic acid was another oxide of niobium. At the present time there is a bitter controversy between two European chemists concerning the existence of a new element, ilmenium, which one of them claims he has discovered, while the other stoutly denies its existence, declaring the ilmenic acid of the first to be a mixture of titanic and niobic acids. Many times have discoveries been announced, and indeed been accepted and believed, until more careful investigation has disproved them. So the time may come when chemists will discover the causes of the differences between nickel and cobalt, iron and chromium, calcium and magnesium, etc., etc., and then they will be able to transmute one into the other.
"But the most important consideration connected with the whole subject is that which presents itself when we speak of the molecular constitution of substances. Let us note here in passing the distinction between an atom and a molecule. An atom is the smallest quantity of an element, indivisible by chemical means, which can exist in a compound body; a molecule is a group of atoms forming the smallest quantity of a simple or compound body which can exist in a free state, or is able to take part in or result from a reaction.[1] Now we are acquainted with many substances that occur in different molecular conditions (allotropic states); that is to say, their atoms are differently grouped under
- ↑ Wurtz. Introduction to Chemical Philosophy.
