532 



ANNUAL REGISTER, I8I7. 



mass probably contains no salt, 

 but what is natural to the sea- 

 water filling its pores. Hence, 

 the generality of ice affords fresh- 

 water, when dissolved. As, how- 

 ever, the ice frozen from sea- 

 water does not appear so solid 

 and transparent as that procured 

 from snow or rain-water, sailors 

 distinguish it into two kinds, ac- 

 cordingly as it seems to have been 

 formed from one or the other. 



Ice frozen from Sea-Water. 



What is considered as salt- 

 water ice, is porous, white, and 

 in a great measure opaque, (ex- 

 cept when in very thin pieces), 

 yet transmits the rays of light 

 with a greenish shade. It is 

 softer, and swims lighter than 

 fresh-water ice, and when dissolv- 

 ed, produces water sometimes per- 

 fectly fresh, and sometimes salt- 

 ish ; this depends in a great mea- 

 sure on the situation from whence 

 it is taken : such parts as are 

 raised above the surface of the sea 

 in the form of hummocks, appear 

 to gain solidity by exposure to the 

 sun and air, and are commonly 

 fresh, whilst those pieces taken 

 out of the sea are somewhat salt. 

 Although it is very probable, that 

 this retention of salt may arise 

 from the sea-water contained in 

 its pores, yet 1 have never been 

 able to obtain, from the water of 

 the ocean, by experiment, an ice 

 either compact, transparent, or 

 fresh. That the sea-water has a 

 tendency to produce fresh ice, 

 however, is proved from the con- 

 centration observed in a quantity 

 exposed in an open vessel to a low 

 temperature, by the separation of 

 the salt from tlie crystals of ice. 



in the progress of the freezing. 

 Thus it is, that in the coldest 

 weather, when a ship exposed to a 

 tempestuous sea is washed with 

 repeated sprays, and thereby co- 

 vered with ice, that in different 

 places obstructitig the efflux of 

 the water overboard, a portion 

 always remains unfrozen, and 

 which, on being tasted, is found 

 to contain salt highly concentrat- 

 ed. This arises from the freezing 

 point of water falling in a certain 

 ratio according to the degree of 

 saltness; thus, though pure water, 

 of specific gravity 1 .0000, freeze 

 with a temperature of 31°, water 

 of specific gravity 1.0263, con- 

 taining about 5| 02. (avoird.) of 

 salt in every gallon of 231 cu- 

 bic inches, that is, with the de- 

 gree of saltnei:S common to the 

 Gieenland seas, freezes at 28J». 

 Sea-water concentrated by fieez- 

 ing, until it obtains the specific 

 gravity of 1.1045, requires a tem- 

 perature of \3~" for its congela- 

 tion, having its freezing point re- 

 duced 18j° below that of pure 

 water ; and water saturated with 

 sea-salt remains liquid, at a tem- 

 perature of — 4°. 



Thus, we are presented Avith a 

 natural process for extracting salt 

 from the sea, at least for greatly 

 facilitating that process in a con- 

 centration of the sahne particles, 

 by the agency of frost. 



When salt-water ice floats in 

 the sea at a freezing temperature, 

 the pro]iortion above, to that be- 

 low the surface, is as 1 to 4 near- 

 ly ; and in fresh water, at the 

 freezing point, as 10 to 69, or 1 

 to T nearly. Hence, its specific 

 gravity appears to be about 0.8*3. 

 Of this description is all young 

 ice as it called, which forms a 

 considerable 



