642 PHYSICAL PROPEETIES OF ICE. 



little formed at a low temperature ; but, no matter at what 

 temperature formed, a part of the remaining salt is expressed as the 

 ice contracts and becomes closer. 



Having thus found that sea-water ice loses some of its saline 

 constituents, I endeavoured to find out what became of the 

 remainder. I have above spoken of the white crystals formed 

 on the surface, called efflorescence ; on testing this, I found that 

 it contained a considerable portion of the ejected salts. This 

 eflaorescence formed at all temperatures, from a little below the 

 freezing point of water to the lowest temperature observed ; this 

 also in character, density, and amount, varied with the tempera- 

 ture at which formed, its density increasing according to the 

 degree of cold. In the act of freezing, some of the saline particles 

 were squeezed out of the ice and forced to the surface, there 

 becoming crystallized if the cold were sufficiently intense, but, 

 if not, only part forming crystals, the remainder forming a pasty 

 semi-fluid understratum. This efflorescence appeared, sooner or 

 later, according to the temperature, but generally commenced 

 when the ice was about fths of an inch thick ; from this period 

 until the ice was from 4 to 9 inches thick, more or less was forced 

 out ; when it attained the latter thickness, this exudation ceased, 

 as the upper portion of the mass had now become too compact 

 and too consolidated to allow of its protrusion. At temperatures 

 above zero, the amount of efflorescence was small, not always well 

 crystallized, and scattered over the surface, being slow of appear- 

 ance, and taking a long time to crystallize ; whereas at low 

 temperatures there was an abundant crop, well crystallized, and 

 covering thickly the whole extent of surface. To test the 

 residuary mass of water after the ice had been formed, so as to 

 determine the amount, if any, of salts expressed into it, set No. 3 

 was instituted. By exposing sea-water to different temperatures 

 in a large tub, and testing the residue after the ice was taken off, 

 I found it contained some considerable portion of the expressed 

 salts ; this portion being dependent on the temperature and length 

 of exposure. On many of these occasions I found on the surface 

 of the ice a pasty fluid, being the liquid efflorescence not yet 

 crystallized. Baron Wrangell, in his Travels, noticed this extra 

 saltness of the crystals found on the surface, but attributed it to 

 evaporation. Now, this cannot be the case, as evaporation is less 

 in proportion to the cold, whereas the amount and density of the 

 efflorescence increased in proportion to the cold. By exposing 

 the residuum of the first freezing of salt-water to a second, a 

 residue was obtained, containing much more salt, and by a con- 

 tinuance of freezing this residue or its residue, a concentrated 

 brine was obtained, no limit being apparent, so far as my experi- 

 ments were made. This set of observations led to another. No. 2. 

 Finding that some of the salts were precipitated, I tried to form 

 fresh water by a similar exposure of sea-water, and, thawing and 

 exposing the ice thus formed three or more times, I succeeded in 

 obtaining water of a density of r0025 and 1 -0020, these results 

 being dependent on the time of exposure andtem perature. Oppor- 



