The flow of liquid colloids through a capillary tube is always slow compared with the now of crystalloid solutions, so that a liquid-transpiration tube may be employed as a colloidoscope. The ultimate pectization of silicic acid is preceded by a graduai thickening in the liquid itself. was observed during the formation of the C per centjelly. silicic acid is brought about in an hour or two, and that of a 2 per cent silicic acid in two days. By contact with pounded graphite, which is chemically inactive, the pectization of a 5 per cent. The pectization of liquid silicic acid is expedited by contact with solid matter in the form of powder. Dilution no doubt weakens the colloidal character of substances, and may therefore allow their crystallizing tendency to gain ground and develop itself, particularly where the crystal once formed is completely insoluble, as with quartz. 1 can only imagine that such crystals are formed at an inconceivably slow rate, and from solutions of silicic acid which are extremely dilute. The formation of quartz crystals at a low temperature, of so frequent occurrence in nature, remains still a mystery. 1 may add, however, that no solution, weak or strong, of silicic acid in water has shown any disposition to deposit primordia puge

This change may be brought about by time alone. The liquidity of silicic acid is only affected by a change, which is permanent (namely, coagulation or pectization), by which the acid is converted into the gelatinous or pectous form, and loses its miscibility with water. A less hydrated jelly than the last mentioned is still less soluble and, finally, when the jelly is rendered anhydrous, it forms gummy-looking white masses, which appear to be absolutely insoluble, like the light dusty silicic acid obtained by drying a jelly charged with salts, in the ordinary analysis of a silicate. of silicic acid gives a solution containing about 1 part of acid in 10,000 water. of silicic acid, gives with cold water a solution containing about 1 part of silicic acid in 5000 water a jelly containing 5 per cent. The jelly of silicic acid may be more or lГ©sa rich in combined water, as it is first prepared, and it appears to be soluble in proportion to the extent of its hydration. We have no degrees of solubility to speak of with respect to silicic acid, like the degrees of solubility of a salt, uniess it be with reference to silicic acid in the gelatinous condition, in which it is usually looked upon as destitute of solubility. Hydrated silicic acid, for instance, when in the soluble condition, is, properly epeaking, a liquid body, like alcohol, miscible with water m all proportions. THE prevalent notions respecting solubility have been derived chiefly from observations on crystalline salta, and are very imperfectly applicable to the class of colloidal substances. ON THE PROPERTIES OF SILICIO ACID AND OTHER ANALOGOUS COLLOIDAL SUBSTANCES.ДЇrom the Journal of

Primordia puge