Am^™n;mlrm-)>  a-  and  $-Eucaine.  197 
Tannic  acid  (1  :  10)  gives  no  precipitate  or  only  a  very  slight 
transparent  flocculency. 
Picric  acid  (1  :  100)  yields  a  fine  lemon-yellow  precipitate  in  solu- 
tions stronger  than  1  per  cent.,  which  is  soluble  in  acids,  but  in 
dilute  solutions  yields  no  precipitate.  Even  in  moderately  strong 
solutions  the  precipitate  formed  by  the  first  drop  or  two  of  reagent 
redissolves.  The  precipitate  with  a-eucaine  is  more  insoluble  than 
either  of  the  others,  and  comes  down,  accordingly,  in  somewhat 
more  dilute  solutions. 
Iodine  in  alcohol  yields  a  brown  precipitate  soluble  in  excess. 
Fr5hde's  reagent  (sulphomolybdic  acid)  gives  no  precipitate. 
Mercuric  chloride  |  1  :  20)  gives  no  precipitate  in  dilute  solution, 
but  in  moderately  strong  solutions  gives  a  fine  white  precipitate, 
easily  soluble  in  excess. 
Ferric  chloride  and  potassium  ferricyanide  mixed  give  no  pre- 
cipitate except  a  white  one  in  strong  solutions.  Allen1  states  that 
cocaine  gives  a  precipitate  of  Prussian  blue,  but  I  have  not  been 
able  to  obtain  it.  Ferric  chloride  is  stated  by  some  authors  to  turn 
red  on  boiling  one  or-  two  drops  of  a  dilute  solution  with  cocaine* 
owing  to  the  formation  of  benzoate  of  iron.  But  as  it  also  turns 
red  with  either  of  the  eucaines  or  simply  with  distilled  water  the 
reaction  is  of  no  value.  It  gives  no  precipitate  even  in  strong  solu- 
tion. 
Cadmium  iodide  gives  a  white  precipitate. 
Potassium  ferrocyanide  gives  in  solution  of  about  10  per  cent, 
a  slight  colorless  gelatinous  precipitate.  A  saturated  solution  of 
(3-eucaine  does  not  yield  this  precipitate  probably  because  the  solu- 
tion is  too  weak. 
Potassium  ferricyanide  gives  a  white  precipitate  in  moderately 
strong  solutions,  which  is  more  easily  thrown  down  if  solution  is 
acid  with  hydrochloric  acid. 
Potassium  bromide,  chloride,  or  bromate  give  no  reaction. 
If  a  few  drops  of  a  solution  of  either  of  the  hydrochlorides  of  a- 
or  (5-eucaine  or  cocaine  be  acidified  with  strong  nitric  acid,  evapo- 
rated to  dryness  in  a  watch-glass,  and  treated  with  one  or  two 
drops  of  a  solution  of  alcoholic  potash,  a  very  characteristic  odor  of 
benzoic  ethyl  ester  is  obtained.  This  reaction  would  probably  also 
be  given  with  other  alkaloids  containing  the  benzoyl  group. 
1  "'  Commercial  Organic  Analysis,"  Vol.  Ill,  Part  II,  p.  275. 
