80  Dielectric  Constants  of  Non-conducting  Liquids. 
The  following  values  for  K  were  obtained  in  three  sets  of 
observations  (temp.  =  12°*5)  :  — 
Set  (1)  of  5  observations  Mean  =  2*071 
Set  (2)  of  4  „  „     =2-027 
Set  (3)  of  5  „  „     =2-049 
Total  Mean  =  2-049 
Drude*  gives  the  value  K  =  2*18  at  17°;  Turnert,K  =  2*20 
at  14°;  but  neither  of  these  observers  purified  their  samples 
or  give  physical  data  as  criteria  of  purity. 
Ethylene  Chloride. 
Purchased  of  Kahlbaum,  portion  on  distillation  at  boiling- 
point  83°*71± -15  at  Bar.  757-1  (corr.)  collected;  D.  4/4  = 
1-27536  (corr.). 
Thorpe  %  gives  the  values  B.P.  =  83°'5  at  Bar.  753*9  and 
D.  4/4  =  1-27432  (corr.)  One  set  of  five  observations  gave 
the  value  of  K= 11'29  at  17°. 
Turner!  gives  K=  10*98,  but  no  details  of  purification  or 
physical  data. 
Monochlorobenzene. 
Purchased  of  Kahlbaum,  portion  on  distillation  at  boiling- 
point  131°-55  +  -2  at  Bar.  736*97  collected  ;  D.  4/4  =  3*12355. 
Ramsay  and  Young  §  give  the  value  B.P.  =  132°at  Bar. 
758-8,  Young  ||  D.  0/0  =  1*12786. 
One  set  of  seven  observations  gave  the  value  of  K  =  10'95 
at  10°*  8  ;  a  previous  observation  for  this  substance  does  not 
appear  to  have  been  recorded. 
The  necessity  for  purifying  halogen  organic  compounds 
before  determining  their  dielectric  constants  appears  to  have 
been  overlooked  ;  most  of  such  compounds  decompose  slowly, 
though  slightly,  in  the  presence  of  sunlight  with  liberation 
of  traces  of  the  halogen  acid,  which  would  impart  a  conduc- 
tivity to  the  liquid,  and  thereby  render  useless  determinations 
of  the  dielectric  constant,  except  possibly  by  the  method  of 
Kernst.  Thus,  to  select  an  example,  the  constant  for  chloro- 
form has  been  determined  by  three  observers,  none  of  whom 
*  Zeits.f.  physikal.  Chem.  xxiii.  p.  309  (1897). 
t  Ibid.  xxxv.  p.  428  (1909). 
\  Journ.  Chem.  Soc.  1880,  Trans,  p.  182. 
§  Ibid,  ]885,  Trans,  p.  654. 
||   Ibid.  1889,  Trans,  p.  488. 
