304     ON  SOME  PREPARATIONS  OF  THE  U.  S.  PHARMACOPOEIA. 
their  patients  require  economy  in  expenditure,  to  employ  this 
agent,  which  costs  only  one-fourth  the  price  of  the  quinia  salt. 
Collodium. — This  formula  is  analogous  but  different  from  that 
of  1850,  both  in  proportion  of  ingredients  and  in  manipulation. 
Mialhe's  plan  of  getting  the  nitric  acid  by  sulphuric  acid  and 
nitrate  of  potassa  is  still  adhered  to,  yet  direction  is  given  as  to 
temperature  and  time  of  maceration ;  the  latter  increased  from 
four  minutes  to  twenty-four  hours.  The  proportion  of  ether  is 
reduced  from  forty  fluidounces  to  twenty-one  fluidounces,  and 
the  quantity  of  alcohol  increased  from  one  to  six  fluidounces ; 
and  the  ether  now  used  is  the  stronger.  An  improvement,  ori- 
ginally suggested  by  the  late  Win.  W.  Livermore,  consists  in 
washing  the  moist  cotton  with  alcohol,  to  dehydrate  it  before  so- 
lution in  alcoholic  ether.  There  is  also  an  alternative  process  by 
which  the  collodion  may  be  made  from  dried  gun-cotton.  The 
details  of  this  formula  were  suggested  by  Dr.  Squibb  ;  the  pro- 
duct is  much  more  consistent  than  the  old  preparation,  and  is 
not  filtered  unless  the  cotton  contains  foreign  fibres  that  con- 
taminate the  product,  when  a  coarse  cloth  should  be  used. 
Collodium  cum  Cantharide. — This  is  one  of  the  new  officinal 
preparations,  though  in  use  for  several  years.  Originated  in  St. 
Petersburg  by  M.  Hisch,  its  use  has  gradually  spread  until  it  is 
now  recognized  in  our  Pharmacopoeia  as  a  means  of  vesication. 
The  menstruum  differs  from  that  in  ordinary  collodion,  first,  in 
containing  none,  or  but  little  alcohol ;  and,  secondly,  in  the 
modification  produced  by  a  large  quantity  of  fatty  oil  extracted 
by  the  ether  from  the  cantharides,  and  which  modifies  its  con- 
tractile property.  The  presence  of  thia  oil  is  undoubtedly  im- 
portant as  a  menstruum  to  liquify  and  render  more  active  the 
cantharidin  present  in  the  coating  on  the  part  to  which  it  is 
applied.  In  operating  on  a  large  scale,  some  chemists  have 
preferred  to  exhaust  the  cantharides  with  a  sufficiency  >  of  ether, 
distill  off  the  ether  to  semifluid  extract  and  dissolve  this  in  suffi- 
cient collodion  to  make  the  proper  measure  of  the  recipe. 
With  tight  apparatus  for  percolation,  and  stronger  ethei,  the 
directions  of  the  Pharmacopoeia  are  quite  sufficient  to  produce  an 
efficient  preparation. 
