## 2 Materials and Methods  
### Properties Affecting the Separation/Calibration Process  
In general, the separation of a mixture into its component parts is possible if they have properties (characteristics) that distinguish (differentiate) them. In particular, seed cleaning and sorting are based on those properties that most differentiate the components of the seed mixture, and which are the basis of the appropriate separation methods. In order to specify the separation methods and the respective working bodies, the properties by which the components of a seed mixture differ the most must be specified. These characteristics are found among the physical-mechanical properties of the seeds that vary widely depending on crop, variety, moisture, etc. The shape and dimensions of the seeds are characterized by the ratio between length, width, and thickness; by the number of planes of symmetry; and by the absolute value of the dimensions, which are of a great variety. Corn seeds are part of the flat-shaped seeds, but their shape is complicated by the presence of ribs, grooves, etc. Physical purity--represents the percentage content of pure seed in relation to the total mass of the analyzed sample and by extension of the lot it represents. Mass of 1000 seeds--gives indications on the size of the seeds and is of particular importance for agricultural practice because the mass of 1000 seeds is taken into account when calculating the amount of seeds per hectare. It varies from species to species and within the species from variety to variety or from hybrid to hybrid. Hectoliter mass--represents the mass of one hectoliter of seeds. The hectoliter mass is influenced by the moisture content of the seeds, the content of impurities and their nature, and on the nature of the basic product characterized by:  
- the specific mass of the seeds;  
- seeds coating;  
- pericarp thickness (seeds coated with pericarp have smaller hectoliter mass due to a lower unit weight--for corn, the hectoliter mass is between 72 and 77 kg). Unit weight--represents the weight of the unit volume of the seed material; it varies within wide limits and depends on the chemical composition and anatomical structure of the seeds, the degree of maturity, moisture, and the amount of air contained in the seed. The unit weight values of corn seeds are between 1.3 and 1.4 (gf/cm\({}^{2}\)) [32]. Seed moisture--for the purpose of good preservation, the seeds must have a water content below a critical level. Moisture is determined directly by oven drying and indirectly with the electronic moisture meter. Porosity--represents the totality of the spaces occupied by air between the solid parts of the seed mass and is expressed by the percentage ratio between the volume of the inter-granular space and the total volume of the seed mass. Flowability--natural slope angle--represents the ability of seeds and seed mass to flow when dropped on an inclined surface or in the open air. For corn seeds, the natural slope angle has values between 30 and 40 degrees, and the flow angle has values between 19 and 30 degrees [22; 29]. Aerodynamic properties--take into account the different resistances to movement of the seeds in an air current. The aerodynamic properties can be characterized by the floating speed of the seeds. The floating speed depends on the weight, surface condition, and geometric shape of the particles that form the components of the seed mixture. Elastic properties--seeds have the property of returning to their original shape after deformation, a property called elasticity. The elasticity is appreciated by the collision restitution coefficient (\(K\)) equal to the ratio of the speeds after the collision (\(V_{2}\)) and before the collision (\(V_{1}\)), in a centric collision. \[K=\frac{V_{2}}{V_{1}} \tag{1}\]  
This coefficient can be determined experimentally by letting the seeds fall (with no initial velocity) from a height \(H\) onto a hard surface and measuring the height \(h\) of lift after impact.