972 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



" It appears, then," saj'S Professor Guthrie, " that under these condi- 

 tions the freezing' of sea-water is little more than the freezing of ice, 

 and that the almost undiminished saltness of the imiiressed ice is due, 

 as suggested by Dr. Eae, to the entanglement amidst the ice-crystals of 

 a brine richer in solid constituents than the original water itself. Such 

 brine, which is here squeezed out in the press, drains in nature down 

 from the upper sui-face of the ice-floe by gravitation, and also is re- 

 l^laced by osmic action Ijy new sea- water which again yields uj) fresh 

 ice; so that while new floes are porous and salt, old ones are more com- 

 pact and much fresher, as the traveller observed. . . . The degree 

 of saltness of a floe depends not only upon its age, but also upon the 

 rapidity with which it was at first formed, and upon the lowest temper- 

 atiu^e to which it has subsequently been exposed." 



Mr. Guthrie justly supposed that the ice of the sea is mainly formed 

 at or near the surface by radiation from the surface into space, and by 

 contact with the colder air. He imitated this by hanging a blackened 

 tin pan, containing a freezing-mixture, within one-eighth of an inch of 

 the surface of the sea-water and thus obtained the ice which, on being 

 pressed, contained a minimum solid residue. 



CONCLUSION. 



It had been my intention to enter into i)ractical details concerning re- 

 frigerators, refrigerator-cars, and the methods of making pure ice eco- 

 nomically. The time and space occupied preclude this now, but the 

 opportunity for giving a connected history of the numerous efforts made 

 of late years to extend the benefits of refrigeration for man's wants will 

 not be neglected, if only in the fishing interests. 



Washington, October, 1879. 



