INVESTIGATIONS on the velocity of crystallisation have been concerned chiefly with the influence of the conditions of the liquid phase, such as the degree of supersaturation o r superfusion and the presence of foreign substances. It seemed desirable to develop a method that would eliminate these influences, in order t o isolate the factors which are concerned with the surface receiving the crystalline deposit. Where the surface has been taken into account by previous experimenters, it has been

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... ssumed that the velocity of crystallisation is proportional to the area of the surface exposed to the liquid. The method employed was to hang in a slightly supersaturated solution of potassium alum two weighed alum crystals as nearly perfect as possible. The solution being stirred and the temperature slowly falling, the crystals grew very regularly and rapidly. A t the end of about fourteen hours the crystals were taken out, dried, and weighed. From the increase in weight the relative thickness of the layer of substance deposited could be calculated. The same crystals were subjected t o a series of such periods of