18 A CONTRIBUTION TO THE STUDY OF ICE-STRUCTURES 



developed into grotesque forms by additions of firmly adhering snow (see Plate IV, 

 Fig. 2). 



A further case worthy of note was that which was presented in a cavern of a large 

 " snow-berg " held in the floe near Cape Barne. The berg, though rather a small one, 

 was originally of the table-topped class. All that was exposed above the sea was 

 fine granular neve, firmly consolidated in the lower portions. Owing chiefly to 

 weathering of the summit, it rose somewhat out of the water during the winter, and 

 exposed a large cavern that had formerly been eaten out below sea -level by the wash of 

 the water. Near the water-level, sixty feet below the summit, the berg was composed of 

 fine granular particles averaging one -thirtieth of an inch in diameter, whilst many 

 of the grains reached a twentieth of an inch in diameter. Though well compacted, 

 the neve in that part of the berg was sufficiently porous to have been saturated with 

 sea-water. So it happened that, as the berg rose, the brine kept oozing from the roof of the 

 cave, developing well -formed stalactites (see Plate IV, Fig. 1). 



When the photograph was taken the temperature was -30° F., and there was but a 

 slight drip, which completely froze on the floor as mamillary stalagmites having the 

 appearance of white enamel — evidently frozen cryohydrate. The stalactites showed the 

 usual rings in cross-section, were resinous in appearance, and exhibited a conchoidal 

 fracture. Towards their downward extremities the internal appearance changed to 

 that of a fine granular texture. To what extent this was due to adhering drift- 

 snow or to the freezing of certain cryohydrates with higher freezing-point was not 

 ascertained. 



V. A COMPARATIVE STUDY OF ICE-CRYSTALLISATIONS 



FROM VAPOUR 



The amount of water vapour necessary to produce saturation in the atmosphere 

 varies with the temperature. Approaching the freezing-point, 32° F., it sinks to a small 

 fraction of what it is at higher temperatures. Below freezing-point, saturation is 

 attained when there is little more than vestiges of water vapour in the air. In a land 

 where almost all is ice, notwithstanding the fact that at such low temperatures the 

 capacity of the atmosphere for moisture is trivial, great results follow from the offices 

 of the atmosphere in taking up, transporting, and depositing H 2 0. For the most part 

 it is evaporation of a solid and deposition as a solid, and is thus a case of sublimation. 



An experiment was entered upon with the object of ascertaining whether vapourisa- 

 tion is accelerated in the case of saline ices. A metal mould for casting cylindrical blocks 

 of regular dimensions was made. In it a series of blocks was cast, each about two 

 pounds twelve ounces in weight. There was a block of fresh-water ice, and others with 

 certain ingredients added in molecular proportions : e.g. NaCl, Na,S0 4 , KC1, MgS0 4 , 

 and MgCl 2 . The blocks were suspended on gibbets on the south side of the Hut, as 

 shown in Plate XCI, Vol. I. What with the interference of an occasional blizzard and 

 certain inherent difficulties the experiment was not altogether a success. However, 

 sorting over the results of a large number of weighings, one is struck by a general 

 accordance indicating more rapid ablation in the saline ices. 



A theoretical consideration of the case suggests that the presence of salt might 

 accelerate evaporation in the region of the temperature scale not far below the 

 freezing-point of fresh water, but that its effect in this respect would be lost at 

 lower temperatures. 



