A HISTORY of almost any common material could be made the framework of a general history of civilization, both in its political and economic aspects, and hence could serve as a kind of heuristic method of teaching general history. This would be a very uneconomic method, since every specialist author would have to repeat a large mass of material already traversed by every other author ; and it may be suggested that a historian of science or technology might profitably assume that the political history (taking the name in its widest sense) with which his studies bring him more or less intimately in contact can be sought elsewhere. There are notable exceptions to this ; some works on the history of science, such as Meyer's "Geschichte der Botanik", deal in detail with various aspects of general history in a way which makes them still very useful to the professional historian when he happens (as is rarely the case) to know of their existence. The history of alum is a subject which lends itself very well to a plan of fitting it into a general picture of the conditions and movements of the times traversed, and an author working up this subject has a good opportunity of doing this if he feels inclined towards it. It may be said that Dr. Charles Singer has, in fact, incorporated a substantial amount of such material, including a general history of the alum trade, in his recently published account*, and this will make it especially valuable and interesting to the general historian.