318 PETTERSSON, ON WATER AND IGE. 



in the water of the warm Atlantic stream. We can therefor& 

 safely imagine the following cycle to take place. 



Siippose a quantity of ice, say 1 kgr, to melt at 45° Lat. 

 N. and the issuing water to be transported with the Atlantic 

 current np to the western coast of Spitzbergen, where it at 

 last solidifies by the influence of the winter cold and is after- 

 wards brought back again Avith the arctic current to 45° Lat.^ 

 there to melt once more in the heated water of the Gulf-stream. 



If the latent heat absorbed by the melting of 1 kgr. of 

 ice, at 45° Lat., was identically equal to the amount of heat 

 set free by the freezing of the seawater, at 75° or 80° Lat., th& 

 whole result of the imaginary process, chosen as example, 

 would be a transport of about 79.2 Calories from the 45"' 

 to the 80'^ parallel. In this case the transport of the heat 

 must be performed by some external force, due either to the 

 trade winds or to the abundant supply of river water to the 

 Mexican Gulf, which causes the niveau of the water there to 

 stånd higher than in the arctic sea. ^ 



We know from the foregoing, that the ice, which arrives 

 so far to the south as to 45° Lat., is relatively pure and only 

 contains a very little amount of salt, consisting principally of 

 chlorides and sulphates. The latent heat absorbed at its mel- 

 ting (= Q) therefore must be a trifle less than 79.25 Calories. 

 If the water of the ocean did not contain any salt, we might 

 expect an identically great amount of heat to be developed 

 by the freezing of 1 kgr. of water at 80° Lat., provided that 

 it was not over-cooled before Jreezing. 



By the saltness of the ocean the character of the process 

 is essentially changed. The latent heat (= R) developed at 

 the freezing of salt water is, as will be seen from the second 

 table of this chapter, very inferior to that of fresh water. 

 Even if we do not take into account the diminution of th& 

 latent heat caused by the dissolved salt (which is however 

 very considerable), we must admit, that: 



R < Q, 

 because the maximum temperature [T = — 2° C or — 1°.9 C] 

 of freezing ocean- water is considerably loiver- than the melting 



1 The difterence of level at the equator and at the pole ought to be 

 about 2 metres, according to Colding [Skand. Nat. Forskare-Sällsk. Möte 

 1863, Bilaga D] and Guldberg [Polyt. Tidskrift, 3, 1872]. 



^ As a thermometer immersed in a mixture of snow and sea-water,, 

 which is constantly stirred, indicates — l^^.s C, we may regard this as the 

 upper limit of the freezing- and the nether limit of the melting-temperatures 



