Am.  Jour.  Pharm.\ 
August,  1896,  J 
Acids  Contained  in  Plants. 
439 
IDENTIFICATION  AND  SEPARATION  OF  THE  PRINCIPAL 
ACIDS  CONTAINED  IN  PLANTS.1  — 
By  L,.  Lindot. 
The  reactions  which  enable  us  to  distinguish  the  vegetable  acids 
are  not  numerous  and  often  uncertain  in  their  application ;  and  if 
we  can  characterize  tartaric  acid — thanks  to  the  insolubility  of  its 
potassium  salt  in  the  mixture  of  alcohol  and  ether — we  are  more 
embarrassed  if  it  is  requisite  to  isolate  the  other  acids,  and  espe- 
cially the  citric  and  malic,  so  frequently  present  in  vegetable 
tissues. 
When  studying  the  compounds  of  these  acids  with  quinine  and 
cinchonine,  I  have  found  that  the  resulting  salts,  and  especially  the 
acid  salts,  present  differences  of  solubility  in  methylic  alcohol,  such 
that  it  is  easy  to  distinguish  citric  and  malic  acids  and  to.  separate 
them  from  vegetable  juices. 
(i)  Cold  methylic  alcohol,  at  950  Gay-Lussac,  dissolves  only  0  3 
percent,  of  acid  quinine  citrate;  so  that  if  we  add  quinine  to  a 
methylic  solution  of  citric  acid,  at  2  or  2-5  per  cent.,  this  alkaloid  is 
dissolved  at  first,  giving  then  rise,  on  stirring,  to  a  bulky  crystalline 
precipitate  of  acid  citrate,  which  may  extend  to  9-3  per  cent,  of  the 
theoretical  quantity.  An  excess  of  quinine,  with  reference  to  the 
composition  of  the  acid  salt,  redissolves  the  precipitate  and  then 
ultimately  the  neutral  citrate  crystallizes  ;  its  solubility  is  greater 
than  that  of  the  acid  citrate,  and  rises  to  3-3  per  cent. 
Under  identical  conditions  the  acid  quinine  malate  (solubility  in 
cold  methylic  alcohol  at  95 0  Gay-Lussac,  8-2  per  cent.)  and  the 
neutral  malate  (solubility  8  0  per  cent.)  remain  in  solution.  The 
presence  of  malic  acid  slightly  interferes  with  the  precipitation  of 
acid  quinine  citrate,  and  when  in  a  mixture  of  the  two  acids  the 
quantity  of  malic  acid  represents  25,  50,  100  or  200  per  cent,  of  the 
quantity  of  citric  acid,  the  weight  of  the  acid  quinine  citrate 
obtained  is  not  more  than  99,  97,  94  or  89  per  cent,  of  the  citrate 
which  would  be  obtained  in  a  liquid  free  from  malic  acid. 
Under  the  same  conditions  the  acid  quinine  oxalate  (solubility 
9-2  per  cent.)  and  the  neutral  oxalate  (solubility  8-2  per  cent.) 
remain  equally  in  solution  ;  but  the  oxalic  acid  increases  the 
solubility  of  quinine  citrate  in  larger  proportions  than  does  malic 
acid. 
1  Chemical  News,  June  26,  1896,  from  Comptes  Rendus,  123,  1185. 
