of some of the Esters at Low Temperatures. 487 



The frequency- o£ the oscillations used was throughout of 

 the order of 4' 7 x 10 5 per sec. 



It will be seen from the above tables that the values of the 

 dielectric constants of these esters when measured at the 

 temperature of liquid air are throughout considerably less 

 than the values obtained at ordinary temperatures. These 

 low values are characteristic of the solid state, for the general 

 course of the change of the dielectric constant with decrease 

 of temperature is first an almost linear rise of the value 

 of the constant as the temperature falls until the melting- 

 point is reached, then a sudden fall during solidification to a 

 value less than thi.it obtained at ordinary temperatures, then 

 a very slow rise as the temperature is further decreased. 

 This phenomenon is illustrated by the case of n-butyl acetate, 

 for which the results obtained for the dielectric constant 

 throughout the range of temperature 292° A-80° A are given 

 below. That this is probably a general phenomenon is 

 shown by the work of several investigators, as, for example, 

 that of Abegg and Seitz on p-azoxyanisole (Zeitsch. Pliys. 

 Cliem. xxix. p. 491, J 899) and various alcohols {lid. xxix. 

 p. 242, 1899). This almost linear rise in the value of the 

 dielectric constant with decrease in temperature is in agree- 

 ment with the theory of the temperature variation of this 

 constant put forward by Debye (Phys. Zeit. xiii. pp. 97- 

 100, Feb. 1, 1912) on the basis of the assumption of the 

 presence of " dipoles " in the liquid dielectric. 



Returning to the tables, it will be seen that, though the 

 values of the dielectric constants at ordinary temperatures 

 of the corresponding members of the series of formates and 

 acetates are distinctly different, they become approximately 

 equal at low temperatures. This would seem to show that 

 at these low temperatures the acid radicle contributes very 

 little to the value of the dielectric constant. 



An inspection of the table will also show that the ratio of 

 the dielectric constant of any member of either series to that 

 of the next higher member does not remain throughout the 

 series the same at low temperatures as it is at ordinary 

 temperatures. 



In Table II. are given the results obtained for the case of 

 n-butyl acetate for the range of temperature 292° A-80° A. 

 The temperatures were obtained by surrounding the vessel 

 holding the experimental condenser bv air (292° A), ice 

 (273° A), freezing mixture (264°-5 A-258°'7 A), solid C0 2 

 and ether (200°'5A), and liquid air (77° 6 A) Readings 

 were taken at each of these temperatures, the results in the 

 table being mean values. Readings were also obtained when 



