The Romance of Modern Chemistry

ELEMENTS WITH DOUBLE IDENTITY a different number of atoms. Since we are dealing with one and the same element, the atoms in the two cases must be the same in kind, but there may be more of them in the one case than in the other. There is, however, another possible explanation. We must remember that not only are atoms grouped to form molecules, but molecules are massed together to form the substance as it presents itself to our eyes. If the hordes of molecules are arranged in regular fashion, then we get a crystalline substance; if they are arranged anyhow, we get an amorphous substance—that is, one without form. So with phosphorus, the molecules may be marshalled differently in the two varieties. Of the two explanations which may thus be given for the existence of phosphorus in two distinct forms, the latter is the more probable. Red or amorphous phos- phorus differs from yellow phosphorus, not in having a different number of atoms in the molecule, but in that the molecules are arranged differently in the two cases. A most interesting and more familiar example of an clement occurring in different forms is furnished by carbon. There are no less than three modifications of this element, two of which at least are as the poles asunder in respect of outward appearance and com- mercial value. It is indeed difficult to realise that dull, amorphous carbon, in the forms of charcoal or lampblack, is the same element as the brilliant, flashing diamond. Yet so it is; while, in addition to these two modifications of carbon, there is a third, quite distinct from both, and variously known as graphite, black-lead, or plumbago. Graphite is a little more distinguished-looking than char- coal, but is mean and commonplace in comparison with the diamond. The three forms of carbon, however, differ not 53