reason, misunderstood. It is evident from the law of the indestructibility of matter that as the iron increases in weight in its conversion into rust, the latter must be a more complex substance than the iron itself, and its formation is due to a reaction of combination. We might form an entirely wrong opinion about it, and might, for instance, consider rust to be a simpler substance than iron, and explain the formation of rust as the removal of something from the iron. Such, indeed, was the general opinion prior to Lavoisier, when it was held that iron contained a certain unknown substance called ‘phlogiston,’ and that rust was iron deprived of this supposed
- Copper carbonate (in the form of a powder, or as the well-known green mineral called ‘malachite,’ which is used for making ornaments, or as an ore for the extraction of copper) changes into a black substance called ‘copper oxide’ when heated to redness.15 This black substance is also obtained by heating copper to redness in air—that is, it is the scoria or oxidation product of copper. The weight of the black oxide of copper left is less than that of the copper carbonate originally taken, and therefore we consider the reaction which occurred to