Whitney, on the other hand, suggests that grains of sand and clay carry down mechanically the particles of fine silt and clay as they settle in a turbid liquid in a beaker; and it is often difficult to wash out a trace of fine material from a large amount of coarse particles, for this reason, although there may be no trace whatever of flocculation. =184. Destruction of Floccules.=—The destruction of the natural floccules is seen in the ordinary process of puddling earth or clay. It is also the result of violent agitation of water or of kneading or boiling, or, finally, to a certain extent, of freezing. All these agencies are employed by the workers in clay for the purpose of increasing the plasticity which depends essentially upon the finest possible condition of the material to be worked. As an illustration of this, Hilgard cites the fact that any clay or soil which is worked into a plastic paste with water, and dried, will form a mass of almost stony hardness. If, however, to such a substance one-half per cent of caustic lime be added, a substance which possesses in an eminent degree the property of coagulating clay, the diminution of plasticity will be obvious at once, even when in a wet condition. If now the mass be dried, as in the previous case, it is easily pulverized. This is an illustration of the effect of lime upon stiff lands, rendering them more readily pulverulent and tillable. The conversion of the lime into a carbonate in the above experiment by passing bubbles of carbonic acid through the mass while still suspended in water does not restore the original plasticity, thus illustrating experimentally the fact known to all farmers that the effect of lime on stiff soil lasts for many years, although the whole of the lime in that time has been converted into carbonate.