Haber, and Bohm and Niclassen16 could detect no crystalline structure in the freshly precipitated zirconium hydroxide nor in the hydroxide which had been precipitated and dried below 400°. No x-ray analyses of the aged sol have been reported, although Weiser17 points out that aged sols usually assume micro-crystalline form while the corresponding hydrous oxides when first prepared are entirely amorphous.The authors are indebted to Dr. C. Harvey Sorum and Dr. Fred Hazel for numerous suggestions during this investigation, and to Dr. Hazel also for valuable assistance in making the Ph determinations. Summary 1. Zirconium oxide hydrosols have been prepared and heated to temperatures up to 275°.2. Measurements have been made on their relative viscosity, flocculation value, Ph and intensity of scattered light.3. High temperature was found to produce a decrease in viscosity, flocculation value and Ph, and an increase in the intensity of scattered light.4. The data presented indicate that the sols heated to higher temperatures are less hydrated than those heated to lower temperatures.

It is difficult to ascertain from the literature1 exactly what are the optimum conditions for the air activation of charcoal, or exactly what happens during the processes of activation. Attempts at activation in a current of air are easily frustrated by a lack of attention to detail or to conditions in different parts of the mass of the charcoal. Similarly, so numerous are the factors involved that occasionally an exceptional success is achieved which it may prove impossible to duplicate.The present studies have been carried out over a series of many years, first with charcoal derived from redwood (Sequoia Sempervirens), as studied by Dr. F. Carlyle Harmon, and then by one of us (R.F.S.) with sugar charcoal, which is practically the only source of highly active, ash-free

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