0. D. von Engeln — Studies on Ice Structure. 467 



tem of grooves. Apparently the melting of the ice in air and 

 sea water is diametrically opposite with respect to the relative 

 rate of the process at the centers of the grains and their inter- 

 crystal zones. The theory of the common ion seems best to 

 fit the case of melting under sea water. In solutions so dilute 

 that dissociation is approximately complete, the solubility of a 

 given electrolyte will be lowered by the addition of a solution 

 containing an ion common to it and the electrolyte, and con- 



Fig. 8. 



ii 





■*}< -•*&- 



S *jK 



&*Edtt^l* i'^v-^i •'.>&« 







^ v 







rr ■ -"- ■ 



i ■' 'i;*- 



Fig. 8. Iceberg, stranded at low tide, with "hammered silver" sur- 

 face developed by melting in sea water. Note the polygonal granules hol- 

 lowed at the center. Photographed Aug. 2, 1909, Yakutat Bay, Alaska. 



versely, the solubility of one salt may be increased by the 

 presence of another salt not containing a common ion. The 

 sea water contains dissociated Na and CI ions, hence the solu- 

 bility of the saline interstitial film is decreased while that of 

 the pure, H 2 0, ice crystal centers is increased. The develop- 

 ment of the "hammered silver" surface by such differential 

 solubility probably requires the maintenance of favorable and 

 rather delicate equilibrium of temperature in that the sea 

 water needs to be at or near the freezing point of fresh water. 



