Letter | Published:

The Dust of Krakatão


ON January 13 I collected a sample of snow from an open field, and examined under the microscope the residue left by its evaporation. This residue showed a number of objects which are not usually found in atmospheric dust. Great precautions were taken to prevent the entrance of dust during evaporation, the vessel being kept covered with filter-paper. Crystals of common salt were very abundant. There were numbers of rather large prismatic crystals, colourless, insoluble in water, and doubly refracting. But the most characteristic objects were minute granules, transparent, colourless, and scattered in thousands all over the field of the microscope. These were insoluble in water. Many black particles were visible and some of these were attracted by the magnet. In fact, when the magnet was swept slowly over the residue, its poles became covered with fine black crystalline particles, evidently magnetic oxide of iron. However, there are large iron-works in this vicinity, which may account for the presence of the magnetic dust. To determine this and other interesting points, it is my intention to examine the snow and rainfall regularly during the next twelve months at least.

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