YELLOW  AMORPHOUS  OXIDE  OP  MERCURY,  ETC.  263 
folds  of  the  mucous  membrane,  and  there  set  up  a  caustic  action, 
which  was  rather  prejudicial  than  otherwise  to  the  subsidence  of 
the  disease.    I  became  positive  of  this  fact  from  some  experi- 
ments I  instituted  with  this  substance,  which  was  first  reduced 
by  many  hours'  trituration  to  as  fine  a  powder  as  possible,  using, 
as  a  vehicle,  fat,  which  melted  quickly  from  the  natural  warmth 
of  the  conjunctiva.    Thus  the  remedy  was,  by  the  movements  of 
the  lids,  equally  distributed  over  the  diseased  surface  ;  and  at 
the  same  time,  the  probability,  or  rather  the  possibility,  was 
avoided  of  any  irritation  being  produced  by  its  remaining  too 
long  in  the  conjunctival  sac.    Even  these  experiments  yielded 
by  far  more  favorable  results.    But  the  ointment  was  rendered 
still  more  perfect  when  I,  acting  under  the  advice  of  Dr.  Hoff- 
mann, substituted  the  yellow  amorphous  oxide  of  mercury.  This 
preparation,  which  up  to  that  time  (1856)  had  found  no  place  in 
the  pharmacopoeia,  but,  as  well  known  to  chemists,  possesses  the 
great  advantage  of  being  in  a  state  of  the  finest  possible  division, 
prepared,  as  it  is,  by  precipitation  ;  and  being  altogether  desti- 
tute of  any' crystalline  form,  it  does  not,  like  the  red  precipitate, 
adhere  to  the  conjunctival  tissue  by  any  fine  points  and  angles. 
But  this  preparation  differs  materially  not  only  in  form,  from 
those  which  have  hitherto  been  employed,  but  also  in  its  chemical 
properties,  which  explain  and  render  intelligible  the  results  ob- 
tained in  practice.    I  may  be  permitted  to  give  the  preparation 
of  the  ointment  in  Dr.  Hoffmann's  own  words: — 
"  Two  forms  of  oxide  of  mercury  are  recognized  : — 
1st.  The  crystalline  or  red  oxide,  prepared  by  the  dry  method, 
and  commonly  known  as  red  precipitate,  constituting  the 
very  common  remedy  ;  and 
2d.  The  amorphous,  or  yellow  oxide,  prepared  by  the  wet 
method  by  precipitation  ;  up  to  within  a  few  years  un- 
known to  the  pharmacopoeia,  although  it  is  indubitably 
preferable  to  the  first. 
The  common  red  precipitate  is  rendered  applicable  to  practice 
by  be^ng  triturated  in  a  porcelain  mortar  till  no  more  brilliant 
crystalline  points  can  be  perceived  :  a  powder  is  thus  obtained, 
which  is  quite  soft,  and  when  rubbed  between  the  fingers  no 
longer  imparts  any  gritty  feel.    If  this,  after  being  prepared  in 
