44  COMMERCIAL  HYDRARaYRUM  CUM  CRETA. 
duced  into  each  bottle,  and  the  mixture  shaken  for  six  hours  ; 
thirtj-one  pounds  of  precipitated  chalk  is  now  made  into  a  uni- 
form paste  with  four  and  three-quarter  gallons  of  water,  and 
the  shaken  mercury  is  added  to  the  mixture  of  chalk  and  water 
and  thoroughly  stirred ;  it  is  now  transferred  to  a  muslin  strainer, 
drained,  dried  and  powdered.  The  advantage  possessed  by  this 
process  is  protection  from  oxidation,  the  honey,  which  was 
originally  added  to  facilitate  the  division,  envelops  the  globules, 
protects  them  as  soon  as  divided,  and  the  small  quantity  left  in 
the  preparation  effectually  shields  the  mercury  from  change,  as 
will  be  shown  by  some  experiments  further  on. 
For  the  purpose  of  testing  the  quality  of  the  preparations 
formed  in  commerce,  samples  were  obtained  from  all  of  the  known 
manufacturers  in  this  country,  and  one  sample  made  by  an  Eng- 
lish manufacturer,  from  the  San  Francisco  market,  which  is 
principally  supplied  with  the  English  product.  The  samples 
were  from  Powers  and  Weightman,  Rosengarten  &  Sons,  Qharles 
Ellis  Son  &  Co.,  Charles  Pfizer  &  Co.,  Herrings  &  Co.,  and  Dr. 
E.  R.  Squibb,  and  three  samples  from  the  dispensing  bottles  of 
pharmacists,  in  Philadelphia  and  ISiew  York.  The  process  of 
assay  adopted  was  that  proposed  by  Dr.  E.  R.  Squibb,  and  pub- 
lished in  the  American  Journal  of  Pharmacy  for  Sept.,  1857. 
Ten  grammes  of  the  powder  was  put  in  a  six  ounce  beaker 
and  75  c.  c.  of  distilled  water  added  and  mixed  with  the  powder  ; 
40  c.  c.  of  pure  acetic  acid  was  slowly  added  at  intervals  with 
stirring.  Considerable  care  is  necessary  to  prevent  the  mixture 
from  frothing  over,  hence  the  expedient  of  first  mixing  the  pow- 
der with  water  ;  the  carbonic  acid  is  liberated  more  readily  and 
the  bubbles  of  gas,  on  account  of  having  a  thinner  film  surround- 
ing them,  are  broken  by  the  stirrer,  and  the  gas  set  free  with 
much  more  ease  than  when  the  acetic  acid  is  digested  alone  with 
the  powder,  and  a  dense  solution  of  acetate  of  lime  formed  that 
envelops  the  escaping  bubbles,  which  are  difficult  to  break,  and 
if  not  broken  the  mixture  froths  over,  and  the  assay  is,  of  course, 
lost.  The  mercury  was  allowed  to  subside  and  the  supernatant 
liquid  poured  on  to  a  small  tared  filter  prepared  for  it,  the  mer- 
cury being  poured  on  last ;  the  filter  was  then  washed,  dried,  and 
weighed.    On  examining  the  contents  of  the  filter  after  being 
