OCR Text |
Show - 3- provided with a thermocouple at sample bottom and at the black disk. The plastic container was placed in a household freezer unit, resting on an aluminum plate maintained at minus 23° C throughout the experiment, and beneath a black aluminum plate heated by an adjustable electric lamp. A strong temperature gradient developed in the snow samples, and they were left exposed to this condition for sixteen days. Some fluctuations of temperature occurred during the first five days, during which the samples settled t © : approximately half their original volume. For the next eleven days the thermocouples indicated that the bottom and top ( black disk) temperatures averaged - 12.7° and - 6.0° 0, respectively. With the sample thickness varying from 3 to Z » 3 cm, the average gradient was 2.7° 0/ cm. Chemicals used in the tests were organic liquids selected on the basis of suitable freezing points and volatility, those chosen being liquid at ordinary snow cover temperatures and of moderate volatility. The reason for this choice was the limitation of the tests to those ciemieals which could be conveniently applied in the field should such testing prove desirable, and which could provide an adequate supply of vapor without being quickly lost from the snow cover by evaporation and diffusion. The individual chemicals used in the first experiment are identified in the results below. Experimental Results The size and quantity of depth hoar crystals generated by the experiment are both smaller than might be expected in nature under a similar temperature environment. Previous tests using these small sample" volumes in the Sfurae freezer unit gave similar results. Quite possibly the small |