It absorbs water easily until a definite state of saturation has been reached, after which it becomes impervious unless the proportion of water is so large and the time of exposure so great that the material falls to an irregular mass which may be converted into a slurry of uniform consistency by gently stirring it. With a moderate amount of water, pelinite develops sufficient plasticity to enable it to be modelled with facility, but clayite and some specimens of pelinite are somewhat deficient in this respect. The pelinitic particles usually possess the capacity to retain their plasticity after being mixed with considerable proportions of sand or other non-plastic material and are then said to possess a high binding power (p. 28).
If a large proportion of water is added to a sample of clayite or pelinite and the mixture is stirred into a slurry it will be found to remain turbid for a considerable time and will not become perfectly clear even after the lapse of several days. Its power of remaining in suspension is much influenced by the presence of even small amounts of soluble salts in either the water or the clay substance, its precipitation being hastened by the addition of such salts as cause a partial coagulation of the colloidal matter present. Some specimens of clayite and pelinite retain their suspensibility even in the presence of salts, but this is only true of a very limited proportion of the substance. In most cases the presence of soluble salts causes the larger particles to sink somewhat rapidly and to carry the finer particles with them.
The rate at which a slip or 'cream' made of elutriated clay and water will flow through a small orifice is dependent on the viscosity of the liquid and this in turn depends on the amount of colloidal material present, _i.e._ on how much of the clay (pelinite) is in a colloidal form. Its viscosity is greatly affected by the addition or presence of small quantities of acid or alkali or of acidic or basic salts. Acids increase the viscosity; alkalies and basic salts, on the contrary, make the slip more fluid. Neutral salts behave in different ways according to the concentration of the solution and to the amount of clay (pelinite) present in the slip. If the slip contains so little water as to be in the form of a thin paste, neutral salts usually have but a small action, but when the slip contains only a small proportion of clay (pelinite) the presence of neutral salts will tend to cause the precipitation of the clay. In this way salts act in two quite different directions according to the concentration of the slip.