256  Congealing  Point  of  Oil  of  Anise.  {AmMay?Sarm- 
when  at  absolute  rest  are  capable  of  being  cooled  many  degrees  below 
their  normal  point  of  congelation  without  becoming  solid.  But  when 
a  liquid  solidifies  after  being  cooled  below  its  normal  freezing  point, 
the  solidification  is  accompanied  by  a  disengagement  of  heat,  which  is 
sufficient  to  raise  its  temperature  from  the  point  at  which  solidification 
begins  up  to  its  ordinary  or  true  congealing  point.  This  physical  law 
and  its  application  to  anise  oils  is  the  key-note  of  my  communication 
this  evening.  The  solidifying  points  of  star-anise  oil  hitherto  quoted 
have  been  abnormal  ones,  due  to  their  determination  whilst  the  fluid 
was  at  rest.  The  true  congealing  point  is  the  temperature  to  which 
the  thermometer  immediately  rises,  on  this  solidification  taking  place. 
The  oil  of  pimpinella  does  not  present  such  a  marked  difference  in 
respect  of  its  abnormal  and  true  congealing  points,  but  as  I  will  pro- 
ceed to  show,  that  of  star-anise  presents  a  strange  dissimilarity. 
Table  A. 
Source  of  Oil. 
Abnormal 
solidifying 
point. 
True 
solidifying 
point. 
Color  reaction 
with  alcoholic 
HC1. 
Fahr. 
Fahr. 
31 
52 
Yellowish  brown. 
Star  anise  (own  distillation). 
24 
49 
Yellowish  brown. 
Star  anise  (direct  import  from 
Macao,  China)  
34 
56 
Pale  brown. 
Star-anise  (broker's  sample). 
36 
54 
Brown. 
Anise  fruit (  German)  
50 
59 
Manganese  pink. 
Manganese  pink 
Anise  fruit  (own  distillation) 
50 
59 
(fading  quickly). 
Table  A  will,  I  think,  show  that  the  margin  allowed  by  the  Phar- 
macopoeia for  the  pimpinella  oil,  viz.,  from  50°  to  60°  F.,  is  prac- 
tically the  difference  between  the  abnormal  and  normal  solidifying 
points,  and  is  therefore  correct,  but  that  the  congealing  point  quoted 
for  star-anise  oil  is  its  abnormal  one,  and  is  therefore,  I  think,  incor- 
rect. Moreover  that  between  the  true  or  normal  solidifying  points  of 
pimpinella  and  illicium  oils  there  is  practically  no  difference,  and  it  is 
only  between  their  abnormal  congealing  points  that  a  wide  divergence 
exists. 
How  then  are  we  to  frame  "  characters  and  tests  "  that  will  dis- 
tinguish these  oils  ?  Either  (1)  we  must  say,  that  the  solidifying  point, 
taken  when  the  liquid  is  at  rest,  of  "  pimpinella  "  oil  is  about  50°  F., 
