Ajanuarr>,Pi906m'}      Inorganic  Chemistry  of  the  U.S. P.  27 
MgO  +  H2S04  =  MgS04  +  H20. 
2)40-06  2)98. 
20-03  49  =  IOOO  c.c.  normal  V.  S. 
•02003  gramme  1        "       "  " 
Magnesii  Sulphas  should  contain  not  less  than  99-7  per  cent,  of 
pure  magnesium  sulphate  (S0202Mg  -j-  7H20);  no  method  for 
assaying  is  given.  Tests  for  limit  of  sodium  and  for  chloride  have 
been  discarded.  The  time-limit  test  for  heavy  metals  and  modi- 
fied Gutzeit's  test  for  arsenic  are  used. 
Lead  Salts.- — Very  few  and  minor  changes  are  noted.  The  test 
for  presence  of  nitrate  in  Plumbi  Iodidum  is  a  decided  improvement 
upon  the  old  test.  In  the  present  test  I  gramme  of  the  salt  is  heated 
with  5  c.c.  of  water,  the  liquid  filtered  into  a  test-tube  of  the  capacity 
of  40  c.c,  5  c.c.  of  potassium  hydroxide  T.  S.  are  added  and  o-2 
gramme  aluminum  wire  introduced.  Then  a  pledget  of  purified 
cotton  is  inserted  in  the  upper  part  of  the  test-tube,  and  a  piece  of 
moistened  red  litmus  paper  placed  over  the  mouth  of  the  tube.  The 
tube  is  now  heated  on  a  water-bath  for  fifteen  minutes.  No  blue 
coloration  of  the  paper  should  be  discernible. 
Potassium  Salts. — Definite  standards  of  purity  are  assigned  in  each 
case.  The  assay  processes  are  practically  the  same  as  in  the  old 
Pharmacopoeia,  though  slightly  modified  ;  half-normal  sulphuric  acid 
V.  S.  being  employed  for  neutralization  instead  of  the  normal  acid 
solution.  Potassium  cyanide  is  assayed  by  a  new  method,  i.  e.,  that 
described  under  acidum  hydrocyanicum.  As  regards  the  tests  for 
identity  it  is  noted  that  sodium  cobaltic  nitrite  T.  S.  has  been  dis- 
carded as  a  test  for  potassium,  and  sodium  bitartrate  T.  S.  and 
tartaric  acid  are  used  instead.  The  only  exceptions  are  in  the  cases 
of  potassium  bitartrate  and  potassium  cyanide,  in  which  sodium 
cobaltic  nitrite  are  still  used,  and  in  the  case  of  Rochelle  salt  in 
which  acetic  acid  is  employed  to  precipitate  the  potassium  as  bitar- 
trate. In  the  case  of  potassium  chlorate,  platinic  chloride  T.  S.  is 
used  in  addition  to  the  tartaric  acid  T.  S.  The  reaction  to  litmus 
paper  is  stated  in  the  case  of  the  potassium  salts  as  being  alkaline 
or  feebly  alkaline,  potassium  bitartrate  is  acid,  and  several  of  the 
salts  are  neutral. 
As  to  the  tests  for  impurities,  "  the  time  limit  test  for  heavy 
metals"  is  recommended  in  most  cases,  instead  of  the  old  sulphide 
