The Romance of Modern Chemistry

 CHAPTER V ELEMENTS WITH A DOUBLE IDENTITY IN the study of chemistry one constantly encounters puzzling phenomena, the interpretation of which involves much patient labour on the part of the investigator. One of these puzzling things is the fact that some substances which are undoubtedly elements have a way of appearing in different forms according to the circumstances under which they are produced. We know that an actor plays sometimes one part, sometimes another; but although his get-up differs from time to time, it is always the same man underneath. So an element may be found masquerading in the garb of strange, unwonted properties, which are apt to deceive the onlooker, and it is one of the triumphs of chemical science that by its penetrating methods it has been able to identify a given kind of matter however it may be masked. To begin with, it is found that some substances are like the chameleon, which can change the colour of its skin, or like the mountain hare, whose fur is brown in summer and white in winter. Such substances exist in two forms of different colour. It is not only in regard to colour, however, that the two modifications differ; their other properties are quite distinct also. A good illustra- tion of this is furnished by phosphorus, which was referred to in a previous chapter as one of the elements which occur in nature always in a state of combination, and 50