100 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

 CHAPTER V

 TESTS MADE UPON CLAYS

 The methods of testing clays are now fairly well standardized and are somewhat uniformly followed with the result that clay technologists and investigators have a reliable basis upon which to-compare the properties of various clays.
 The measurement of the plasticity of a clay still remains a matter of personal opinion, for no satisfactory means of measuring it has as yet been devised. The terms employed to describe the plasticity of a clay are only relative and will of course vary to some extent with the individual. Plasticity is usually described as "good", "excellent", "poor", "low", etc. A clay having good or excellent plasticity is said to be "fat", and one having low or poor plasticity is described as being "lean."
 The water of plasticity is a more definite factor and can thus be accurately measured. The water of plasticity is the amount of water necessary to give a clay its maximum plasticity. It is expressed in terms of percentage based upon the dry weight of the clay and is determined by weighing a test piece at maximum plasticity and again weighing it after all the moisture has been driven out by first drying at room temperature and finally at 110' C. until it has a constant weight. The water of plasticity test indicates the amount of water necessary td bring a clay to its point of maximum plasticity in which state it can be best worked.
 The shrinkage water is that portion of the water of plasticity which escapes up to the point where air-shrinkage ceases, or in other words, it is the water lost in air-drying. The clay without the shrinkage water is at the point of maximum air-shrinkage in whi&h condition the clay particles are in contact.
 The pore water is that portion of the water of plasticity which remains in the inter-particle spaces after the point of maximum airshrinkage has been reached. It can be driven off only by heating the test pieces to 1100 C. The pore water plus the shrinkage water is the water of plasticity.
 The slaking of clays is the property possessed by them when dry, of crumbling into a flaky or pulverulent mass when immersed in water. In order to determine this property it is necessary to first dry the test pieces at room temperature. -Then all the remaining moisture is driven off by heating them for two hours or longer at 1100 C. They are then