The instrument consists of a brass cup into which a sample of fine soil mixed with water is placed, and a spike designed to make a furrow in the soil being tested. By means of a crank to which it is attached, the cup is repeatedly raised and dropped from a predetermined height onto a base that forms an integral part of the apparatus. The liquidity limit is the water content at which 25 strokes cause the furrow to close over a length of 13 mm.