Vi. remember the translation of the verbs to be and to have: 1. the question is whether mechanical or physical separation methods have to be applied. 2. we know the classification of solids is of great importance in food industry. 3. we have considered the operation of mixing which may be used for a purpose or as an auxiliary operation. 4. to choose the equipment for a certain purpose all properties of the material to be processed are to be considered. 5. this mixer has vertical as well as horizontal material displacement. 6. in some cases the purpose of mixing is to obtain a good contact between the materials to be mixed.