under the same drying conditions. 5. A sample of a porous, manufactured sheet material of mineral origin was dried from both sides by cross circulation of air in a laboratory drier. The sample was 0.3 square and 5 mm thick, and the edges were sealed. The air velocity over the surface was 3 m/s, its dry-bulb temperature was 52°C and its wet-bulb temperature 21°C. There were no radiation effects. The solid lost moisture at a constant rate of 7.5 x 10 kg/s until the critical moisture content, 15% (wet basis) was reached. In the falling-rate period, the rate of evaporation fell linearly with moisture content until the sample was dry. The equilibrium moisture content was negligible. The dry weight of the sheet was 1.8 kg. Estimate the time of drying sheets of this material 0.6 by 1.2 m by 12 mm thick from both sides, from 25 to 2% oisture t-3.575h