YELLOW  AMORPHOUS  OXIDE  OF  MERCURY,  ETC.  265 
acid  and  chloride  of  mercury  ;  whereas  the  red  oxide  undergoes, 
with  chlorine  gas  at  the  ordinary  temperature,  hardly  any  change 
This  difference  of  chemical  behaviour  of  the  two  oxides  consti- 
tutes a  different  degree  of  resistance  to  the  various  agents  they 
are  submitted  to,  and  is  explained  by  their  different  states  of 
cohesion.  In  respect  to  the  use  of  the  yellow  precipitate  for 
eye-ointments,  I  may  be  allowed  to  say  a  few  words  on  the  vehicle 
of  the  ointment.  The  most  perfect  vehicle  for  an  eye-ointment 
must  be  very  soft,  without,  however,  being  too  fluid,  lest  the 
heavy  oxide  sink  to  the  bottom  ;  but  when  in  contact  with  a  mod- 
erate heat  of  the  body,  it  must  completely  melt,  so  that  the  pre- 
paration it  contains  may  become  quickly  and  uniformly  diffused 
over  the  eye.  Besides  this  peculiarity  of  consistence,  the  vehicle 
must  be,  as  far  as  possible,  indifferent  in  its  behaviour  to  the 
oxide,  and  exhibit  the  least  possible  tendency  to  rancidity,  which 
might  exert  a  deoxidizing,  reducing  action  on  the  oxide.  Numer- 
ous experiments  with  hog's  lard,  butter,  glycerine,  glycerine 
ointment,  and  mixed  fats,  have  led  me  to  give  the  preference  to 
the  last;  and  I  recommend  either  the  mixture  of  spermaceti, 
wax,  almond-oil,  and  rose-water,  known  as  'cold  cream,'  only 
omitting  the  water,  as  this  favors  rancidity,  and  substituting  for 
it  quantities  of  almond-oil,  varying  according  to  the  heat  of  the 
weather  ;  or  a  mixture  of  butter,  of  cocoa,  and  almond-oil,  like- 
wise proportionate  to  the  temperature.  In  both  compounds  the 
almond-oil  must  be  as  fresh  as  possible,  and  had  best  be  prepared 
by  the  apothecary  himself."* — Braithivaite  s  Retrospect,  Janu- 
ary^ 1866. 
*  As  regards  the  strength  of  the  ointment,  I  generally  use  one  drachm 
of  oxide  to  one  ounce  of  fat.  This  may  appear  very  strong  to  some,  but 
experience  amply  shows  that,  applied  in  proper  cases,  it  does  not  in  any 
way  irritate  too  much.  Idiosyncrasies  may,  of  course,  be  observed,  as  in 
every  remedy  ;  and  if  the  ointment  in  a  given  case  irritates  to  much,  its 
strength  may  be  reduced  to  30  grs.  of  oxide  to  the  ounce.  I  may  further 
remark,  the  two  constituents  of  the  ointment  must  be  rubbed  up  to  a 
most  intimate  admixture,  if  it  is  to  act  well.  The  following  are,  then,  the 
two  formulae  : — 
Ilydrarg.  oxydat.  flavi,  gr.  xxx.  (via  humida  parati).    Ung.  cetacei, 
^  ss.    Misce  exactissime  et  fiat  unguent.  ;  or. 
R.  Hydrarg.  oxydat.  flavi,  gr.  xxx.  (via  humida  parati).    Ung.  cetacei, 
^j.    M.  exactiss.  et  fiat  ungent. 
