The methods of preparation of the remaining elements depend on considerations of the cost of the
compound from which the element is to be prepared, and on the ease of preparation. In the case of those elements which are required on a commercial scale, like iron, for example, the process of manufacture is regulated chiefly by the cost of the ore, and of the operations necessary to produce the metal in a state of purity sufficient for commercial purposes. But if perfectly pure iron is required for scientific purposes- for example, in order to determine its electrical properties- then the question of cost does not come into consideration, and processes are adopted which are necessarily very costly. In the description which follows, however, we shall give only the ordinary methods of preparation.
Again, the process chosen depends greatly on the physical and chemical properties of the element which it is desired to isolate. Some elements are volatile, and are more or less easily separated by distillation from the material from which they are produced ; some elements are attacked by water, while others resist attack ; some fuse at comparatively low temperatures, and can thus be separated, while others are producible in a compact state only at the enormously high temperature of the electric arc. It is necessary, therefore, to know the properties of the element required before deciding on a process for its isolation. The preparation of the remaining elements will therefore be considered from this point of view.