22  Inorganic  Chemistry  of  the  U.S. P.  {^kini^SS^' 
Calcium  Salts. — A  definite  standard  of  purity  is  assigned  in  the 
case  of  each,  but  no  assay  process  is  given  except  in  the  cases  of 
calx  chlorinata  and  of  calx  sulphurata.  The  latter  is  described  as 
in  the  old  Pharmacopoeia  as  "  a  mixture  containing  at  least  60  per 
cent,  of  calcium  sulphide  (CaS)  together  with  unchanged  calcium 
sulphate  (CaS04)  and  carbon  in  varying  proportions."  The  new 
process  appears  to  be  more  satisfactory. 
Creta  Pmparata  is  described  as  native  calcium  carbonate,  freed 
from  most  of  its  impurities  by  elutriation.  It  is  also  described  as 
being  insoluble  in  water  and  in  alcohol  but  soluble  in  acetic,  nitric, 
or  hydrochloric  acids  with  copious  effervescence,  leaving  not  more 
than  a  trifling  residue.  When  heated  to  full  redness  it  gradually 
loses  carbon  dioxide  and  is  converted  into  calcium  oxide.  Thus  a 
very  indefinite  purity  standard  is  given,  "  trifling  residue "  is  a 
relative  amount  of  residue,  and  may  mean  more  or  less.  Further 
than  above  quoted,  no  tests  for  identity  or  for  presence  of  probable 
impurities  are  assigned.  In  view  of  the  fact  that  Creta  praeparata  is 
largely  used  internally  and  enters  into  Hydrargyrum  cum  creta  and 
Pulvis  creta  compositus,  definite  tests  for  impurities  as  were  given 
in  the  U.S.P.  of  1890  should  have  been  continued.  Tests  for  mag- 
nesium, iron,  sulphate,  and  barium  were  given  in  the  1890  Pharma- 
copoeia. 
1  Cerium  Oxalate. — This  salt,  although  still  prescribed,  has  lost  favor 
to  a  considerable  extent  because  of  its  unreliable  medicinal  action. 
The  commercial  salt  is  not  pure  cerium  oxalate,  in  fact,  the  Pharma- 
copoeia describes  it  as  consisting  chiefly  of  a  mixture  of  the  oxalates 
of  cerium,  didymium  and  lanthanum,  and  of  other  rare  earths. 
No  standard  of  purity  is  assigned,  but  numerous  tests  for  impurities 
are  given.  The  chemical  formula,  Ce2(C204)3  -j-  9H20,  which  was 
given  in  the  1890  Pharmacopoeia  has  been  very  properly  omitted. 
Cupri  Sulphas  is  the  only  official  copper  salt.  It  should  contain 
not  less  than  99-5  per  cent,  of  the  pure  salt. 
Iron  Salts. — Ferri  iodidum  saccharatum,  ferri  lactas  and  ferri 
valerianas,  also  the  liquors  ferri  acetatis,  citratis,  and  nitratis  have 
been  dismissed. 
Ferri  Chloridum  should  contain  22  per  cent,  as  against  20  per 
cent,  of  metallic  iron  in  the  form  of  chloride,  the  chemical  formula 
is  (perhaps  accidentally)  omitted,  though  we  find  it  under  Liquor 
ferri  chloridi.    The  latter  is  prepared  in  the  same  manner  as  before, 
