Mass corresponds to the boundary point, if hitting the cut after the third layer on the bottom of the cup is connected. Another device for determining the border flow consists of a metal cone with a polished surface. The total height of the cone – 25 mm. The vertex angle – 300. At a height of 10 mm from the apex of the cone bears a circular mark 2. Balancing device, consisting of steel beam 3 and the two metal cargo 4, is to sink into a clay cone mass vertically. The total mass of the cone with a counterweight device 76 0,2, the clay mass filled the cup with a diameter of 40 and five deep not less than 20 mm, the surface of the mass wipe out to the edges. Set the bowl on the stand 6 and bring to the surface mass balancer plug (slightly greased with petroleum jelly).
If the cone after 5 seconds., Falling under the influence own weight, fell to the circular marks – the consistency of the clay mass corresponds to the boundary flow. Determination of plastic limit is the following. For the remainder of the previous definition of mass is added a little dry clay mixture is thoroughly mixed and rolled by hand on the glass or marble into a bundle with a diameter of about 3 mm. If at this thickness burn keeps the plastic properties and do not crumble, it is collected into a ball and again rolled out (the mass of highly pre-roll on a plaster board or filtered paper). Lamination should be brought up until a thin bundle of drying soil mass begins to crumble into pieces length of 3-10 mm. After obtaining the desired consistency of the masses, corresponding to the border point and plastic limit, samples are removed (at least 10 g) was placed in pre-dried and weighed porcelain crucibles, weighed and dried to constant weight in an oven at 105-110 0C. The results are recorded in the laboratory register, calculate the absolute and relative humidity, and plasticity number.