146 
COLLODION. 
little  needed,  to  be  called  coUodium  contrahens.  The  first  may 
be  prepared  as  follows : 
Take  of  pyroxylin  or  gun-cotton,  eighty-six  grains. 
Castor  oil,  eighty-six  grains  (or  glycerin,  sixty  grains). 
Stronger  ether,  three  and  a  half  fluidounces,  or  two  troyounces 
and  two  hundred  and  six  grains. 
Stronger  alcohol,  one  fluidounce,  or  three  hundred  and  seventy- 
six  grains. 
Dissolve  the  castor  oil  (or  the  glycerin)  in  the  stronger  alcohol, 
add  the  ether  to  the  solution,  and  dissolve  the  gun-cotton  in  the 
mixture  by  shaking.  Should  it  contain  visible  floating  particles, 
set  it  aside  for  a  few  days,  and  decant  the  collodion  from  the 
sediment.  Collodion  is  a  nearly  colorless  opalescent  liquid,  of 
a  syrupy  consistence,  very  liable  to  loss  by  evaporation,  and 
dangerously  inflammable.  A  small  portion,  say  twenty  or  thirty 
grains,  weighed  in  a  counterpoised  corked  vial,  and  then  exposed 
to  spontaneous  evaporation  by  removing  the  cork  and  laying  the ' 
vial  on  its  side  till  dry,  loses  ninety-one  per  cent,  of  its  weight 
in  four  hours. 
In  comparing  the  formulas  of  some  of  the  modern  Pharma- 
copoeias, no  two  were  found  alike,  and  the  following  are  the 
percentages  by  weight  of  pyroxylin  : 
The  U.  S.  Pharmacopoeia  gives    3-50  per  cent. 
British  "  "      2-60  " 
"    French  "  "       7'00  " 
"    Prussian        "  "       3-  " 
And  the  formula  above  given  5*  " 
of  pyroxylin.  Specimens  of  the  present  officinal  U.  S.  Pharma- 
copoeia Collodion,  of  the  British  "  Collodium,"  and  "  Collodium 
Flexile,"  of  the  French,  of  the  Prussian,  and  of  the  formula  here 
proposed,  are  presented  herewith,  as  well  as  specimens  showing 
the  eff'ect  of  larger  proportions  of  glycerin.  All  have  been  tried 
by  the  writer  upon  himself,  and  that  which  appears  to  yield  the 
most  durable  and  flexible  film  in  summer  w^eather  is  the  collodion 
containing  five  per  cent,  each  of  gun-cotton  and  castor  oil.  It 
is  observed  that  the  smaller  proportion  of  gun-cotton  renders  the 
film  more  contractile,  and  therefore  for  this  variety  the  small 
proportion  of  the  British  Pharmacopoeia  is  recommended.  In 
