Am  Jour.  Pharm.  "I 
Oct.,  1882.  J 
Soluble  Salts  of  Caffeine. 
495 
upon  cooling  it  will  deposit,  not  valerianate  of  cafPeine,  but  siin])ly 
caffeine,  entirely  soluble  in  chloroform  and  only  retaining  mechani- 
cally traces  of  the  acid,  sufficient  to  impart  the  odor.  The  acid 
titrate  of  the  solution  remains  the  same  as  before  the  addition  of  the 
caffeine,  which  proves  clearly  that  the  caffeine  has  not  carried  down 
with  it  a  sensible  quantity  of  the  acid  in  its  precipitation.  Also  when 
caffeine  and  valerianic  acid  are  placed  together  under  a  bell  glass,  as 
in  the  preparation  of  valerianate  of  ammonia,  the  caffeine  only  becomes 
impregnated  with  the  odor  of  the  acid.  I  have  verified  this  fact  upon 
commercial  ^S^alerianate  of  caffeine occurring  in  fine  crystalline  nee- 
dles resembling  those  of  caffeine,  a  character  that  was  very  natural, 
since  it  was  only  caffeine  with  a  valerianic  odor.  Exposure  to  the  air 
^ind  simply  washing  removed  this  odor. 
Lactic  acid  does  not  combine  with  caffeine  to  form  a  lactate.  Syrupy 
lactic  acid,  saturated  in  the  cold  w^th  caffeine  remains  syrupy  indefi- 
nitely ;  and,  as  in  the  case  of  valerianic  acid,  pure  caffeine  crystallizes 
oat  upon  the  cooling  of  a  lactic  acid  solution  that  has  been  saturated 
while  hot. 
It  is  the  same  with  citric  acid,  which  does  not  give  a  citrate.  The 
product  which  is  decorated  with  this  name  is  only  a  mixture  of  caf- 
feine and  acid. 
Another  circumstance  goes  to  prove  further  the  non-existence  of 
these  pretended  salts  of  caffeine  and  organic  acids.  Whilst,  for  exam- 
ple, citric  acid,  which  is  tribasic,  requires  for  the  formation  of  citrates 
three  equivalents  of  base,  one  or  two  of  which  can  be  replaced  by  one 
or  two  equivalents  of  water,  there  is  required  to  effect  the  solution  of 
one  equivalent  of  caffeine  in  water  a  quantity  of  acid  represented  in 
weight  by  about  three  equivalents  of  acid.  The  relations  are,  there- 
fore, precisely  the  inverse  of  those  which  should  obtain  in  the  forma- 
tion of  a  citrate.  To  sum  up,  organic  acids  do  not  form  definite  salts 
with  caffeine.  They  augment,  it  is  true,  its  solubility  in  water,  but 
without  combining  with  it,  and  since  the  acidity  of  the  acids  is  in  no 
way  modified  by  caffeine,  it  will  be  evident  that  with  solutions  of  caf- 
feine in  organic  acids  there  would  be  injected  a  quantity  of  free  acid 
several  times  the  weight  of  the  dissolved  caffeine. 
With  mineral  acids  the  conditions  are  different.  Sulphuric  acid 
forms  with  caffeine  a  sulphate  that  crystallizes  with  difficulty.  Hydro- 
chlori(^  and  hydrobromic  acids  on  the  contrary  form  salts  that  are 
easily  obtainable  in  very  fine  crystals.    These  salts  are  perfectly  defi- 
