116         ON  COLLODION  AND  CANTHARIDAL  COLLODION. 
pharmaceutical  purposes  as  that  prepared  at  a  lower  tempera- 
ture. 
Collodion  Cotton. 
Take  of  nitric  acid,  sp.  gr.  1*42,  one  fluid-ounce ; 
Sulphuric  acid,  sp.  gr.  1*84,  one  fluid-ounce  ; 
Cotton  freed  from  impurities,  thirty  grains. 
Mix  the  acids  in  a  beaker  glass  or  other  convenient  vessel ;  cover 
with  a  plate  of  glass  and  place  it  in  a  vessel  of  cold  water  until 
the  temperature  is  reduced  to  70°  or  80°  Fahr.,  when  remove 
the  glass  from  the  water  and  immerse  the  cotton.  At  the  expi- 
ration of  twelve  hours  wash  the  cotton  with  cold  water  until  free 
from  acid,  and  dry  it  at  a  moderate  temperature. 
Collodion. 
Take  of  Collodion  cotton,  six  grains  or  a  sufficient  quantity  ; 
Stronger  ether,  one  fluid-ounce  ; 
Stronger  alcohol,  one  fluid-ounce. 
Mix  the  ether  and  alcohol  in  a  three  ounce  vial  and  add  the 
collodion  cotton.    Agitate  the  mixture  occasionally  until  the 
cotton  is  dissolved. 
Collodion  paper  has  been  introduced  into  use  by  photographers. 
This  may  be  prepared  in  the  same  manner  as  collodion  cotton, 
by  immersing  strips  of  pure,  thin,  unsized  paper.  It  is  more 
(Easily  washed  than  cotton  and  makes  a  very  pure  and  transpa- 
rent collodion,  using  the  same  menstruum  for  its  solution  as  for 
collodion  cotton.  If  a  sufficiently  pure  paper  can  be  obtained  at 
a  moderate  price,  I  think  it  will  entirely  supercede  the  use  of 
cotton.  Chemically  pure  filtering  paper  answers  the  purpose 
admirably,  while  tissue  paper  does  tolerably  well  but  is  not  so 
good.  I  have  not  succeeded  so  well  with  white  printing  paper, 
owing  probably  to  its  thickness. 
Cantharidal  Collodion. 
Take  of  Cantharides,  in  fine  powder,  a  troyounce ; 
Collodion  cotton,  a  sufficient  quantity ; 
Stronger  alcohol,  a  sufficient  quantity  ; 
Stronger  ether,  a  sufficient  quantity. 
Itloisten  the  cantharides  with  four  fluid-drachms  of  stronger  al- 
cohol and  pack  it  in  a  glass  percolator  of  proper  size,  arranged 
