396  Glycyrrhizin  in  Licorice  Root.        J  ^ji™  Ja? ra' 
acid  by  cooling  to  o°,  is  confirmed  by  myself.  I  noticed  it  particu- 
larly in  the  method  of  Evans'  Sons,  which  will  be  treated  later.  It 
may,  therefore,  be  taken  as  proved  by  this  simple  experiment,  that 
glycyrrhizic  acid  is  less  soluble  in  water  at  o°  than  at  150,  from 
which  one  deduces  the  obvious  application  to  the  analytical  method. 
A  similar  method  for  determining  the  losses  in  the  glycyrrhizin  de- 
termination, due  to  the  solubility  of  the  acid  in  water,  is  described  by 
Durier. 
He  dissolves  the  glycyrrhizic  acid,  which  he  had  precipitated  in 
previous  experiments,  in  25  cc.  water,  and  precipitates  with  hydro- 
chloric acid.  He  filters  and  weighs  the  residue.  The  difference  be- 
tween glycyrrhizic  acid  used,  and  that  finally  weighed  is  considered 
by  him  as  the  solubility  number  in  25  cc.  of  water.  Here  also  an 
error  is  involved.  Durier  does  not  determine  the  solubility  in  water, 
but  in  acidified  water.  These  two  solubility  numbers  are  entirely 
different!    In  discussing  Durier's  work  I  shall  go  into  this  in  detail. 
We  see  that  Haffner,  Durier  and  Capin  have  concerned  them- 
selves with  the  solubility  of  glycyrrhizic  acid,  and  that  all  three,  un- 
der different  experimental  conditions,  arrived  at  quite  different  re- 
sults. Under  these  circumstances  the  question  presents  itself :  Have 
these  experiments  any  object?  Theoretically  it  must  be  obviously  an- 
swered in  the  affirmative,  but  it  is  otherwise  with  the  practical  side 
of  this  question  as  regards  the  application  for  the  present  work. 
First  of  all  the  question  must  be  answered:  Shall  the  solubility  of 
the  chemically  pure  or  of  the  impure  acid  be  investigated?  Haffner 
voices  his  views  as  follows :  " Chemically  pure  acid  does  not  enter 
into  the  practical  question,  therefore  for  the  solubility  determination 
I  use  the  impure  acid."  I  am  of  the  same  opinion.  Xobody  has  yet 
succeeded,  and  in  my  opinion  never  will  succeed,  in  weighing  ap- 
proximately pure  glycyrrhizic  acid  quantitatively.  I  therefore  con- 
sider it  of  no  practical  value  to  determine  how  much  of  the  pure  acid 
dissolves  in  water,  since  one  always  works  with  impure  acid.  One 
always  weighs  "glycyrrhizin  plus  impurity."  Of  this  mixture  the 
pure  acid,  or  the  impurity,  or  a  portion  of  both  may  dissolve  in  water. 
Since  one  weighs  the  impure  acid  it  would  be  inaccurate  to  take  into 
account  only  the  solubility  of  one  constituent  of  the  mixture  of 
glycyrrhizic  acid  plus  impurity,  and  to  neglect  that  of  the  other. 
Judging  from  this  line  of  thought,  one  should  determine  the  solubil- 
