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Show - 2- observed for Ice in the course of generating artificial snow crystals in the laboratory. Kobayashi and Higuchi ( 1937) noted marked effects on crystal growth by minute traces of vapor from silicone waterproofing agents, and cited a similar experience by Nakaya ( 1937). Hallet and Mason ( 1958) observed some similar effects from isobutyl alcohol, and reported a systematic variation of crystal habit ( in artificially generated crystals) with alcohol vapor pressure at a constant temperature. The latter observed that the habit changes reflected changes in the relative growth rates of the basal and prism faces, and noted that the reason for these changes were not clear, although they postulated the surface absorption of foreigft polar molecules, '' possibly?;- by poisoning of dislocation sites". The practical possibilities of depth hoar modification by trace quantities of chemical poisons have led to some trial experiments at the U. S, Forest Service Avalanche Study Center at Alta, Utah. One series of laboratory tests on artificial depth hoar has just been completed, and the results are reported below. Experimental Conditions Freshly- fallen new snow consisting of stellar crystals and a few capped columns was collected in a plastic foam container with six compart- 3 ments, each of 630 cc capacity. Density after collection was 0,05 g/ cm . Two or three drops of a selected organic liquid were added to each of five compartments during collection of the snow sample, the sixth sample being reserved as a control. Thin, black disks, loosely fitting, were placed on the snow surface in each compartment, and were free to follow change of snow surface level with settlement. Each compartment was sealed with a polyethylene sheet and petroleum jelly, and the control sample was |