494 
Soluble  Salts  of  Caffeine. 
Ain..)our.PI>arm. 
Oct.,  1882. 
tobacco-smoke.  The  quantity  of  this  alkaloid  amounts  to  about  0*7 
per  cent,  of  the  weight  of  tobacco  consumed,  and  about  15  per  cent, 
of  the  total  quantity  of  nicotine  contained  in  tobacco.  In  conclusion 
of  the  first  part  of  his  paper,  the  author  criticises  the  researches  of 
Vohl,  Heubel,  Le  Bon,  and  Pease.  He  shows  that  VohFs  opinion  as 
to  the  non-existence  of  nicotine  in  tobacco-smoke  is  without  foundation. 
This  chemist  evidently  disregarded  the  fact  that  nicotine  is  decomposed 
by  w'arm  potassium  hydroxide.  The  remaining  three  publications 
cannot  be  regarded  as  a  satisfactory  solution  of  the  whole  question  of 
oontroversy  of  opinion,  as  they  are  very  incomplete. — Jour.  Chem.  Soc, 
Aug.  1882;  from  Dlngl.  polyt.  J.,  vol.  244. 
SOLUBLE  SALTS  OF  CAFFEINE. 
By  C.  Tanret. 
Hitherto,  in  consequence  of  its  slight  solubility,  caifeine  has  been 
administered  hypodermically  only  in  very  small  doses ;  in  fact,  at  the 
ordinary  temperature,  it  requires  93  parts  of  water  to  dissolve  it,  so 
that  a  cubic  centimeter  Avould  contain  scarcely  more  than  a  centigram. 
Most  of  the  salts  of  caffeine  mentioned  in  therapeutical  works  do  not 
exist,  and  those  that  do  cannot  be  employed,  because  upon  being  dis- 
solved they  are  decomposed  into  acid  and  caffeine,  the  latter  being  pre- 
cipitated if  the  water  is  not  in  the  proportion  required  for  the  solution 
of  the  free  alkaloid. 
The  alkaloidal  properties  of  caffeine  are  extremely  weak  ;  it  is  per- 
fectly neutral  in  its  behavior  towards  litmus,  while  the  ordinary 
reagents  for  alkaloids  do  not  precipitate  it  unless  its  solutions  are  rela- 
tively very  strong.  Not  being  alkaline,  caffeine  is  incapable  of  satu- 
rating the  smallest  quantity  of  acid,  and  although  it  forms  salts  with 
certain  acids  these  salts  are  far  from  being  as  stable  as  those  of  most 
of  the  other  alkaloids,  as  will  be  seen  upon  considering  its  behavior 
with  the  acids  most  frequently  employed. 
Acetic  acid  dissolves  caffeine  freely.  If  this  solution  be  allowed  to 
evaporate  spontaneously  the  acid  volatilizes  entirely  and  there  remains, 
not  a  salt  of  caffeine,  but  pure  caffeine.  An  acetate  of  caffeine,  there- 
fore, does  not  exist. 
Neither  does  valerianic  acid  form  with  it  a  valerianate  of  caffeine. 
If  caffeine  be  saturated  hot  with  a  very  strong  solution  of  this  acid, 
