24  Inorganic  Chemistry  of  the  U.S. P.      { ATan»aryPi1906m' 
Mercnty  Salts. — Definite  purity  standards  are  assigned  in  each 
case,  but  no  assay  method  is  given. 
In  the  case  of  Hydrargyri  Chloridum  Mite  a  new  test  for  the  pres- 
ence of  mercuric  chloride  is  recommended,  namely,  2  grammes  of 
the  mild  chloride  are  shaken  with  20  c.c.  of  ether,  filtered,  the 
filtrate  evaporated,  distilled  water  added,  and  the  solution  tested  first 
with  silver  nitrate  T.  S.,  and  then  another  portion  with  ammonium 
sulphide  T.  S.  This  test  depends  upon  the  solubility  of  mercuric 
chloride  in  ether,  and  the  insolubility  of  the  mild  chloride  in  the 
same  menstruum.  The  test  for  mercuric  chloride  in  calomel,  given 
in  the  old  Pharmacopoeia,  depended  upon  dissolving  it  out  with 
water  or  alcohol,  and  treating  the  solution  with  hydrogen  sulphide 
T.  S.,  or  silver  nitrate  T.  S.  The  new  test  is  a  much  more  delicate 
one.  The  detection  of  other  soluble  impurities  is,  however,  a  much 
more  complicated  procedure  than  was  the  old,  and  its  results  prob- 
ably not  more  reliable.  Arsenic  is  tested  for  by  the  modified 
Gutzeit's  test. 
Liquor  Calcis  is  assayed  by  titration  with  tenth-normal  sulphuric 
acid  V.  S..  instead  of  as  before  with  decinormal  oxalic  acid  V.  S. 
Liquor  Ferri  Chloridi  now  should  contain  29  per  cent,  of  the  anhy- 
drous salt  (FeCl3),  corresponding  to  10  per  cent,  of  metallic  iron, 
while  formerly  it  contained  37-8  per  cent,  of  the  anhydrous  salt, 
corresponding  to  62-9  per  cent,  of  the  crystallized  salt,  or  to  about 
13  per  cent,  of  metallic  iron.  The  method  of  preparation  is  the  same 
as  before,  but  smaller  quantities  of  the  substances  are  taken. 
Liquor  Fern  et  Ammonii  Acetatis  contains  double  the  former 
quantities  of  the  ferric  chloride  and  diluted  acetic  acid  and  iy2  times 
as  much  of  solution  of  ammonium  acetate. 
Liquor  Plumbi  Subacetatis. — This  solution  is  of  the  same  strength 
as  before,  though  10  grammes  more  of  each  of  the  ingredients  are 
taken.  The  old  assay  method  was  one  of  direct  titration  with  nor- 
mal sulphuric  acid  V.  S.,  using  methyl  orange  as  an  indicator. 
This  assay  could  be  quickly  made,  and  the  results  were  sufficiently 
accurate  for  a  substance  which  is  used  almost  entirely  for  external 
application.  The  new  method,  while  more  scientific  and  of  greater 
accuracy  when  performed  by  one  accustomed  to  such  work,  is,  how- 
ever, entirely  too  cumbersome  for  use  by  the  pharmacist  in  assaying  a 
solution  in  which  a  trace  more  or  less  of  the  active  ingredient  would 
be  of  no  moment.    The  assay  directions  are,  if  10  grammes  of  the 
