It consists of a pressure-tight flanged cylindrical measuring bowl, fitted with a removable flanged and a conical cover assembly with a seal in-between. The conical cover has an air valve and a pet cock for bleeding-off the water. A cylindrical stand pipe, which is graduated in percent air content, is fixed on the conical cover assembly. Required pressure is applied to the specimen with the help of a pressure bulb. The whole assembly is mounted on a flat base. Each apparatus is supplied complete with a calibrating cylinder, pressure gauge, funnel, trowel and tamping bar.