Am.  Jour.  Pharm. 
AprU,  1888. 
O71  Coca. 
199 
easily  determined,  since  the  gold  is  rapidly  reduced  to  tlie  metallic  state, 
and  the  silver  chloride  darkens  to  black  instead  of  to  chocolate  or  vio- 
let, as  would  be  the  case  if  it  were  pure. 
In  analytical  determinations  it  is  important  to  digest  the  silver 
chloride  for  a  considerable  time  with  hydrochloric  acid,  and  even  then 
it  is  doubtful  if  the  foreign  chloride  is  entirely  removed,  especially  if 
it  is  ferric  chloride. 
These  observations  show  that  silver  chloride  has  a  great  tendency  to 
combine  with  small  quantities  of  other  chlorides,  and  supports  the  au- 
thor's view  as  to  the  nature  of  the  "photo-salts.^'  They  also  explain 
the  fact  that  a  small  quantity  of  mercuric  chloride  very  greatly  re- 
duces the  sensitiveness  of  silver  chloride  to  light.  In  order  to  ascer- 
tain the  presence  of  mercury  in  the  silver  chloride,  the  author  employs 
a  solution  of  stannous  chloride  in  hydrochloric  acid,  which  has  no  ac- 
tion on  silver  chloride  if  light  is  carefully  excluded,  but  gives  a  brown 
or  brownish-black  color  to  the  precipitate  if  mercury  is  present.  The 
author  was  unable  to  remove  mercuric  chloride  from  silver  chloride 
even  by  very  prolonged  washing. 
Poitevin's  observation  that  his  colored  photographic  images  resisted 
the  action  of  light  better  after  they  were  treated  with  dextrin  and  lead 
chloride  is  explained  by  the  tendency  of  the  lead  salt  to  prevent  alter- 
ation of  silver  chloride. — Jour.  Chem.  Sci.,  1888,^.  109;  Am.  Jour. 
Sci.,  XXXIV.,  p.  384. 
ON  COCA. 
By  Dk.  H.  H.  Rusby. 
From  a  lecture  at  the  Philadelphia  College  of  Pharmacy,  December  1, 1887,  stenograph- 
ically  reported  by  Dr.  C.  H.  Morgan. 
As  an  indigenous  plant  coca  is  perhaps  unknown.  It  frequently  occurs  in  a 
wild  state  and  in  situations  where  escape  seems  to  have  been  impossible.  Yet, 
in  some  such  cases  I  have  traced  its  origin  directly  to  escape  from  cultivation. 
So  it  is  difficult  to  determine  its  origin  in  any  case.  The  varieties  of  coca  are 
two,  the  Peruvian  and  Bolivian.  I  have  here  some  specimens  of  coca  which  I 
gathered  myself  and  I  can  therefore  bear  witness  to  the  accuracy  of  determina- 
tion. The  specimen  which  I  hold  in  my  right  hand  is  Bolivian  coca.  It  is 
the  finest  variety  of  coca  which  exists.  You  will  observe  there  are  two  plants 
represented  on  this  sheet.  One  is  without  leaves,  they  having  been  picked  for 
the  market.  On  the  other  the  leaves  still  exist.  Observe  the  size  and  form  of 
these  leaves,  if  it  is  not  too  far  away  from  you.    This  is  Peruvian  coca 
