252  Pkarmacopceial  Preparations.         {Am  May?if9h7arm' 
For  example,  black  mercurial  lotion  can  be  preserved  in  its  normal 
black  color  by  the  addition  of  5  per  cent,  by  volume  of  glycerin,  but 
I  find  that  10  per  cent,  of  mucilage  of  tragacanth  will  produce  the 
same  result,  and  have  the  advantage,  from  its  viscosity,  of  holding 
mercurous  oxide  well  suspended ;  the  addition  of  both  these  to  the 
preparation  would  be  an  advantage.  It  has  further  been  suggested 
that  glycerin  should  be  used  to  preserve  sublimate  solution,  espec- 
ially the  official  liquor  hydrargyri  perchloridi,  as  it  has  been  thought 
necessary  that  this  solution  requires  preserving,  from  the  chemical, 
not,  of  course,  from  the  biological  point  of  view.  But  both  glycerin 
and  alcohol  added  to  this  solution,  especially  if  exposed  to  light, 
cause  a  reduction  of  the  salt  and  deposition  of  mercurous  chloride, 
as  in  the  official  solution  of  the  Codex,  which  contains  10  per  cent, 
of  alcohol.  Notwithstanding  statements  to  the  contrary,  I  find  that 
a  simple  solution  of  mercuric  chloride  in  distilled  water,  or  even  in 
spring  waters  containing  supercarbonate  of  lime  in  solution,  is  more 
stable  than  it  is  with  a  preservative  added,  especially  one  of  such  a 
nature  as  chloride  of  ammonium  in  the  official  solution.  This,  as 
I  showed  so  long  ago  as  1870,1  instead  of  being  a  preservative,  forms 
a  double  salt  in  solution  (sal  alembroth  plus  an  excess  of  chloride  of 
ammonium),  and  the  solution,  if  prepared  with  common  water  in 
place  of  distilled  water,  or  even  if  prepared  with  distilled  water  and 
diluted,  throws  down  a  quantity  of  one  of  the  white  precipitates  of 
mercury.  To  such  an  extent  is  this  the  case  that  I  found  in  pre- 
paring a  pint  of  the  official  solution  with  new  river  water  in  place 
of  distilled  water,  that  2  7  grains  of  this  precipitete  was  deposited, 
thus  about  one-fourth  of  the  mercurial  salt  was  rendered  insoluble 
in  preparing  the  solution,  and  more  deposited  on  further  dilution 
with  the  water.  In  fact,  a  time  arrived  when  there  was  scarcely  a 
trace  of  mercury  salt  in  solution,  and  as  this  preparation  is  most 
largely  used  in  hospitals  where  common  water  is  always  used  to 
dilute  the  medicines,  it  leads  to  very  discrepant  results  therapeu- 
tically. It  has  also  been  suggested  that  chloride  of  sodium  should 
replace  chloride  of  ammonium  in  the  official  solution,  as  this  salt  is 
largely  used  in  making  the  sublimate  tablets  for  the  convenience  of 
surgeon's  use,  but  I  have  found  that  although  sodium  chloride  helps 
these  tablets  to  disintegrate  readily  it  has  no  advantage,  in  fact  it  is 
detrimental  to  the  keeping  properties  of  the  solution.    I  have  here 
1  Pharmaceutical  Journal,  [2]  Vol.  XI.  p.  544. 
