AmjuTiyUri9^-arm'^  Topical  Applications.  303 
Glycerin  is  generally  used  as  a  solvent  and  in  the  preparation  of 
other  compounds. 
Holocaine  is  the  most  delicate  substance  we  work  with.  Glass 
vessels  should  be  avoided  in  preparing  and  preserving  the  solution, 
as  the  small  quantity  of  the  alkali  derived  from  the  glass  precipitates 
the  drug.    Porcelain  should  be  the  container  of  choice. 
Homatropine  hydrobromide  is  generally  prescribed  in  from  2 
per  cent,  to  3  per  cent,  solution  rendered  sterile. 
Hydrastis.  When  this  preparation  is  written  for  in  liquid  form 
the  colorless  preparation  should  be  dispensed. 
Iodoform.  The  mode  of  preparation  for  ointment  has  been 
previously  described.  When  dispensed  in  powder  form  boracic  acid 
is  the  best  diluent. 
Mercury  is  a  most  important  chemical  in  the  manufacture  of 
ophthalmic  pharmaceuticals.  The  bichloride  of  mercury  and  yellow 
oxide  of  mercury  ointments  have  been  described.  The  other  salts 
of  mercury  are  generally  prescribed  for  internal  use.  Metallic  mer- 
cury is  usually  dispensed  as  mercury  ointment  50  per  cent.  U.  S.  P. 
Pilocarpine  and  its  salts  are  incompatible  with  tannin,  iodides, 
alkalies,  corrosive  sublimate  and  silver  nitrate. 
Potassium  Iodide  is  used  both  internally  and  externally  in  oph- 
thalmic work.  In  ointments  it  should  first  be  dissolved  in  water  at 
saturation  and  then  incorporated  with  wool  fat. 
Physostigmine  or  E serine  solutions  should  always  be  dispensed 
in  dark  bottles.  Solutions  that  have  acquired  a  dark  color  should  be 
rejected. 
Silver  Nitrate  is  used  both  in  crystal  form  and  in  solutions  and 
must  be  dispensed  in  dark  glass. 
Sodium  Borate  is  generally  prescribed  in  solution  as  a  detergent. 
Sulphur,  when  prescribed  in  ointment  form,  should  be  carefully 
incorporated  with  a  white  petrolatum  base. 
Zinc  Salts  are  generally  prescribed  in  solution.  In  the  prep- 
aration of  the  solution  all  borates  must  be  avoided. 
Pipettes  or  medicine  droppers,  for  use  with  ophthalmic  solu- 
tions, should  be  regulated  to  such  a  point  that  one  drop  will  be 
equivalent  to  one  minim.  After  very  many  tests  it  has  been  found 
that  a  dropper  2.2  Mm.  outside  dimension  with  an  opening  1.1  Mm. 
and  the  wall  of  the  glass  barrel  1.1  Mm.  on  each  side  will  form  as 
nearly  as  possible  a  minim  drop. 
Potash-lime  glass  should  be  used  for  this  purpose  as  it  can  be 
worked  more  exactly. 
