2Vlanuals of mineral dressing or more precisely those of comminution-classifi- cation treat in particular the mechanics of the machines, and generally their handling. In this way the plant engineer becomes acquainted with the equip- ment but is given help in learning something of the processes taking place in the material to be comminuted even though the purpose of the operation is to enhance wanted and to avoid unwanted physical or physico-chemical processes. Neglecting the description or representation of generally used and well- kwn equipment the object of this mograph is to supply information on the processes taking place in grinding installations. It explains the sometimes complicated phemonena by applying quite simple means; it requires only an elementary kwledge of mathematics, mechanics and physical chemistry. The ideas are applicable to the grinding of all brittle raw materials or semi- finished industrial products. The special problems of cement grinding and thm;e of hall mills are explained in more detail; in cement grinding we have to meet special requirements with regard to ball mills apart from other con- siderations -, since these w demand the greatest overall energy consumption. Currently disputed problems are dealt with, and naturally the views of the author are given in detail, but contrary views are also mentioned and the ample list of references ensures that these opposing views can be considered.