171 



current: 1200 cm.); that of water at 18° is 81.07 (wave- 

 length practically infinite) as determined by Turner 

 (1900). Ice at the temperature of liquid air has a specific 

 inductive capacity of 1.76 to 1.88 (wave-length : 75 cm.) ac- 

 cording- to Behn-Kiebitz (1904). (For quotations see the 

 Smithsonian Tables.) 



5. Optical Properfies. Ice is birefringent ; the refrac- 

 tive indices, as given by Reusch (1864) are 1.30598 for the 

 ordinary ray and 1.30734 for the extraordinary ray (red 

 light). ■ ' 



V. MELTING AND MELTED MATERIAL 

 A. THE PROCESS OF MELTING 



Although there is an abundant biological literature on 

 the possible injurious and lethal etTects of thawing, the 

 process of fusion itself has been little investigated, far 

 less than the process of freezing. 



Miiller-Thurgau (1881) attempted to study the course 

 of thawing in a few tissues. He established, though with 

 rather crude methods, some thawing curves. These, when 

 compared with the corresponding freezing curves, pre- 

 sented some characteristic ditTerences which later investi- 

 gators discussed in more detail. 



Fischer (1911), after discussing some of the results 

 which he obtained with Bobertag (1909) in freezing and 

 thawing various carbon compounds, analyzed the afore- 

 mentioned results of Miiller-Thurgau. He concluded that 

 the amount of heat liberated in freezing is not the same as 

 that absorbed in thawing and he attributes this dit¥erence 

 to some endo- and exothermic processes concomitant with 

 freezing and thawing. 



Maximow (1914) compared freezing and melting curves 

 of potato tissues and noticed, in particular, that the freez- 

 ing point was more than half a degree lower than the 

 melting point. As to the difference observed by Fischer 

 between the heat liberated in freezing and the heat ab- 

 sorbed in thawing, he showed that it is a question of pro- 

 cedure ; the difference is reversed if one changes the 

 cooling velocity in the freezino- curve. 



