14. Open-ice, or sailing-ice, is where the pieces are so separate as to admit of a ship sailing conveniently among them.
15. Heavy and light are terms attached to ice, distinguishable of its thickness.
16. Land-ice consists of drift-ice attached to the shore; or drift-ice which, by being covered with mud or gravel, appears to have recently been in contact with the shore; or the flat ice resting on the land, not having the appearance or elevation of icebergs.
17. A bight is a bay in the outline of the ice.
18. A lane or vein is a narrow channel of water in packs or other large collections of ice.
When the sea freezes, the greatest part of the salt it contains is deposited, and the frozen mass, however spongy, probably contains no salt but what is natural to the sea-water filling its pores. Hence the generality of ice, when dissolved, affords fresh water. As, however, the ice frozen altogether from sea-water does not appear so solid and transparent as that procured from snow or rain water, the whale-fishers distinguish it into two kinds, accordingly as it affords water that is potable, or the contrary, as it appears to have been the product of fresh or salt water.
What is considered as salt-water-ice appears blackish in the water, but in the air is of a white or grey colour, porous, and in a great measure opaque, (except when in very thin pieces,) yet transmits the rays of light with a blue or blueish green shade. When dissolved, it produces water sometimes perfectly fresh, and at others saltish. This depends, in a great measure, on the situation from whence it is taken; such parts as are raised above the surface of the sea, in the form of hummocks, or which, though below the surface, have been long frozen, appear to gain solidity, and are commonly fresh; whilst those pieces taken out of the sea, that have been recently frozen, are somewhat salt.
Fresh-water-ice of the sailors is distinguished by its black appearance when floating in small pieces in the sea, and by its transparency when removed into the air. Fresh-water-ice is fragile, but hard; the edges of a fractured part are frequently so keen as to inflict a wound like glass. The most transparent pieces are capable of concentrating the rays of the sun, so as to produce a considerable intensity of heat. With a lump of ice, of by no means regular convexity, I have frequently burned wood, fired gunpowder, incited lead, and lit the sailors’ pipes, to their great astonishment, all of whom, who could procure the needful articles, eagerly flocked around me, for the satisfaction of smoking a pipe ignited by such extraordinary means. Their astonishment was increased by observing that the ice remained firm and pellucid, while the solar rays emerging from it were so hot, that the hand could not be kept longer in the focus than for the space of a few seconds. In the formation of these lenses, I roughed them out with a small axe, and then scraped them with a knife, polishing them merely by the warmth of the hand, supporting them during the operation in a woollen glove. I once procured a piece of the purest ice, so large that a lens of sixteen inches diameter was obtained out of it; unhappily, however, the sun became obscured before it was completed, and never made its appearance again for a fortnight, during which time, the air being mild, the lens was spoiled.
All young ice, such as bay-ice and light-ice, which form a considerable part of drift and pack-ice in general, is considered by Greenland sailors salt-water-ice; while fields, floes, bergs, and heavy-ice, chiefly consist of fresh-water-ice. Brash-ice likewise affords fine specimens of the latter, which, when taken out of the sea, are always found crowded on the surface with sharp points and conchoidal excavations.
Ice, when rapidly dissolved, continues solid as long as any remains, but, when exposed to the air, at a temperature of only two or three degrees above the freezing point, its solution is effected in a very peculiar manner. Thus, a large lump of fresh-water-ice, when acted on by such a process, if placed in the plane of its formation, resolves itself into considerable columns of a prismatic appearance. These columns are situated in a perpendicular position, almost entirely detached, so that when a blow is struck with an axe, the whole mass frequently falls to pieces. In the land icebergs, these columns are often of amazing magnitude, so as, when separated, to form floating icebergs.