PHYSICAL PROPERTIES OF ICE. 645 



density varied with tliat of the sohition in which they were found. 

 On breaking this artificial sea-water ice, as well as that naturally 

 formed whilst under two inches thick, I observed that it easily 

 separated into perpendicular laminse, thin, but not long; when 

 viewed with a magnifying glass, presenting the same appearance 

 as that of the plates just mentioned ; the markings noticed on 

 the imder-surface being but the edges of these lamina?, which, 

 being placed side by side, presented a sal ammoniac appearance : 

 in fact, a mere lateral assemblage or buikling up of thin lamina? of 

 ice, the increase being from below on the lower end and under 

 edge of these plates. 



Perhaps the statement of Dr. Kane, that sea- water ice under 

 certain circumstances is completely free from salt, may be ex- 

 plained by the following facts and experiments. After our 

 winter preparations had been commenced, and the pool of fresh 

 water (from melting snow) had been frozen over, the men sent 

 out to bring in snow for culinary purposes brought in some ice 

 instead ; this they obtained from some hummocks near the ship, 

 these hummocks being part of the formation of the previous 

 winter's pack in which we were caught. This ice turned out to 

 be sufficiently fresh for all the purposes of domestic use. On 

 several occasions the party sent out for this ice, digging too deep 

 into the hummock, and not content with the surface pieces, found 

 that the ice was no longer fresh, but quite salt — this ice being a 

 continuation of the same hummock, and also of the previous 

 winter's growth. 



On the 12th and 13tli of August 1857, whilst lying off Browne 

 Islands, and within about four miles of the glacier, surrounded by 

 bergs, I noticed an appearance like oil on the surface of the 

 water ; on closer inspection and testing, this proved to be fresh 

 water floating on the surface of the salt to the depth of two or 

 three inches. The sun, beaming dowm upon the bergs, had 

 melted the ice and snow ; this, running off, floated on the surface 

 and remained separate, so long as there was no wind to mix and 

 agitate the fluids of different densities. To a combination of such 

 circumstances, with an after freezing of this surface water, do 

 these fresh hummocks owe their origin ; the water, being frozen 

 in this state, and afterwards the ice elevated into hummocks 

 afforded us a "drinkable element" during the winter; and when 

 the men had exhausted the supply of top-pieces, they, supposing 

 that all was alike, continued their labours, but were disappointed 

 in obtaining salt-water ice instead of fresh. To make sure of 

 this, 1 took a tub of salt-water, and poured upon its surface, on a 

 glass plate, fresh water, to the thicknei-s of two inches, and 

 allowed the whole to freeze. On testing the upper two inches 

 of ice formed, I found it quite fresh, whilst the under portion was 

 salt. 



