This project was an attempt to deter:nine haw the plasticity of clays and limes, as determined by the Whittemore Plasticimeter, varied over a range of water contents. The performance tests showed that the Plasticity Figure depends on the load applied to the shaft and on the size of the sphere. Furthermore the position of the zero-setting has an important effect on the results of a test. For one clay body, containing Tenn. Ball no. 5, there was a plastic range, at the working consistency of the clay, within which the Plasticity Figure remained constant. For another clay body, containing Challenger Ball, the Plasticity Figure decreased at a steady rate with increase in water content. For both clay bodies the one minute travel was found to be approximately proportional to the water of plasticity. The plasticimeter was found to be applicable to testing limes providing all the load was removed. Two Ohio Whites and one mason's hydrate were tested. In general, the Plasticity Figure was inversely proportional to, and the one minute travel directly proportional to the water content. The Ohio Whites required 15 per cent less water to reach the testing consistency than the ma.son's hydrate, and had Plasticity Figures, at that point, twice as great. A variety of clays were tested and Plasticity Figures obtained for both de-aired samples and those not de-aired. The results of typical tests were expressed on a flow diagram. / M.S.