The upper limit of moisture which keeps the plastic properties of clay, called the boundary flow. With further increase of moisture the clay mass loses its ability to keep the form – it flows. The lower limit of moisture content of clay, which has plastic properties, called the plastic limit. Below this limit, the clay becomes brittle properties. The difference between the moisture content of clay masses in the states 'border flow' and 'plastic limit' quantifies the plasticity and ductility called the number. To perform the analysis of laboratory samples of clay taken away weighed weighing not less than 50 grams, shredded (not rubbing) to complete passage through a sieve with holes of 0.5 mm. The sample is placed in a porcelain cup, stirring continuously to add water until a thick homogeneous plastic mass. Clay mass is uniformly distributed on the bottom of the cup a thickness of 10-15 mm and cut metal spatula into two equal parts so that the gap between them was at the top of the width of 2.5-3 mm, and at the bottom of the cup – 1 mm.

Cup mounted on the upper disc device design and assign Vasiliev holder. A rod device, which is mounted the drive should be raised to a height of 75 mm from the base plate and a screw-mounted holder. After this release the rod so that it is free (under its own weight) was falling on the supporting plate. When you hit a weight in the cup is shaken, and the clearance between its parts is reduced.