OCR Text |
Show - 5- Plot with N- heptaldehyde: Very large depth hoar crystals 6 to 10 mm in diameter were found, with average size around 7 mm. Hie largest crystals appeared near the top of the treated snow layer, just the reverse of natural depth hoar. Note that the two chemicals in this field test apparently exchanged roles as inhibitor and accelerator from those observed in the laboratory. There is good reason to believe that an error was made in the initial identification of the test plots, and the chemical labels were reversed. Uiis is confirmed by persistance of odor in the inhibited plot, a characteristic to be expected of the highly aromatic N- heptaldehyde. In any circumstances, the marked differences in snow types between the test plots indicate that such chemicals do have a significant effect on snow crystal evolution in the field when applied in practical quantities. Review of the Literature A number of authors have reported the phenomenon of chemical poisoning of snow or ice crystals in recent years. In all cases this occurred either accidentally or intentionally with the growth of artificial crystals in the laboratory. Ihe present studies appear to be the first dealing with natural snow in the field. The effects of different chemicals on ice crystal habit as shown by our work and as reported by other investigators are summarized in the following table. It is noteworthy that the effects of a given chemical sometimes differ widely with differences in experimental conditions. This emphasizes the fact that such applications of this phenomenon as the inhibition of depth hoar depend on empirically- determined methods, the physical basis for which are not clearly understood. Erractic or variahle results in the field are quite possible. |