PROPERTIES AND CONSTITUTION OF SEA-WATER, ^-^y 



ors concerning this curious and still little-known fact : "Not every 

 year, but times enough, out on the open sea, I have seen ice come rap- 

 idly up to the surface. If the weather is calm, we can perceive, as 

 far out as we can see, small cakes in the shape of a plate, coming from 

 the bottom, rise to the surface. The edge is in the air, but, when the 

 upper part of the plate gets above the level of the water, the plate 

 turns over and lies flat upon the liquid. It is a dangerous business, 

 for a boat may thus in a few minutes be surrounded by immense masses 

 of new ice," * 



Aside from this anomaly, the formation of isolated blocks of ice in 

 the open sea is very rare. Water of ordinary salinity becomes denser as 

 it cools, for it freezes at about 28° Fahr., and, as we have explained, 

 attains its maximum density at about 35° only if we keep it artifi- 

 cially in the liquid condition. Water that has lost its caloric in con- 

 tact with the atmosphere soon sinks ; sometimes, as Scoresby attests, 

 ice which is formed at medium depth I'ises to the surface, while sound 

 ing thermometers indicate temperatures near or even below the point 

 of congelation at the bottom. Otto Petterssen is of the opinion that, 

 if water submitted to a cold of a few degrees below its freezing-point 

 does not solidify, it is because immobility favors surfusion, or rather, 

 what is very possible, because we do not know all the laws of nature. 



Mr. Petterssen has succeeded by a series of experiments in explain- 

 ing a variety of phenomena which manifest themselves in the boreal 

 seas, and which Arctic explorers have long been acquainted with, with- 

 out understanding the reason of them. Sea-water, after its passage to 

 the solid state, has not the same chemical composition as before ; but 

 besides this change, which we shall speak of again, it has another in- 

 teresting peculiarity. If the temperature is very low, the ice of the 

 ocean, like nearly all known bodies, contracts by cold ; but at a few 

 degrees below the freezing-point, and before melting, it diminishes in 

 volume when heated, and dilates on cooling. Between 14° Fahr. and 

 — 4°, according to the age and source of the block, there is produced a 

 minimum of density, the mass acquiring its maximum volume — that is, 

 the behavior of the solid is the inverse of that of river- water. 



While it contracts by heating at about 18° or 23° Fahr., the ice of 

 salt-water loses some of the properties which it possesses at lower tem- 

 perature, and which are common to it with ordinary ice. It has no 

 longer the vitreous aspect, the fragility, and the homogeneity of solid 

 ice, but becomes softer, more i:)lastic, and less transparent ; its frac- 

 ture is less distinct, and cracks and holes multiply in it. And, when 

 brackish water congeals, it loses its disagreeable taste, but its bad looks f 

 and want of limpidity deprive it of commercial value. 



Sea-water is a very complex saline solution ; chemical analysis dis- 

 covers in it halogen radicals, simple, as chlorine and bromine, or com- 



* We owe these details to the kindness of M. Otto Tetterssen, who has furnished us 

 with many interesting facts, the fruits of his personal observations. 



