ANoVembef,hi9or}      Inorganic  Chemistry  of  the  U.S.P.  519 
Although  the  Pharmacopoeia  directs  that  the  salt  should  contain 
not  less  than  99  per  cent  of  the  pure  salt,  it  gives  no  assay  method. 
It  enters  into  the  preparation  of  the  effervescent  sodium  phosphate. 
Strontti  SahcylaSy  Strontium  Salicylate  (Sr(C7H503)2  -f-  2H20)  It 
should  be  not  less  than  98-5  per  cent,  purity.  It  is  soluble  in  18 
parts  of  water  and  in  66  parts  of  alcohol.  In  the  U.S.P.  of  1890 
strontium  bromide,  iodide  and  lactate  were  official,  in  the  present 
revision  the  lactate  has  been  dropped,  and  the  salicylate  (a  much 
better  preparation)  has  been  introduced. 
The  Pharmacopoeia  describes  eight  tests  for  identity,  and  for  the 
detection  of  impurities  recommends  the  time-limit  test  and  a  test 
for  barium.  The  assay  is  a  gravimetric  one,  depending  upon  the 
conversion  of  the  salt  into  strontium  sulphate.  It  may  also  be 
assayed  volumetrically  by  neutralization  after  ignition. 
Talcum  and  Talcum  Purificatum  are  both  official.  The  former  is 
native  hydrous  magnesium  silicate,  in  powder  or  masses.  It  is  also 
official  in  the  German  Pharmacopoeia.  Talcum  purificatum  is  to  be 
found  in  the  National  Formulary,  and  is  used  as  an  aid  in  filtering 
turbid  liquids  containing  finely  divided  matters  in  suspension  which 
are  apt  to  pass  through  the  filter  or  to  stop  up  its  pores.  It  is  used 
in  the  U.S.P.  method  of  preparing  official  waters  of  volatile  oils,  in 
the  same  way  as  in  previous  revisions  of  the  U.S.P.  there  was  used 
magnesium  carbonate,  then  absorbent  cotton,  and  then  precipitated 
calcium  phosphate. 
Talcum  purificatum  is  prepared  from  native  talcum  by  treatment 
with  hydrochloric  acid. 
Unguentum  Acidi  Borici  contains  10  per  cent,  of  boric  acid  in  a 
base  consisting  of  white  petrolatum  with  10  per  cent,  of  paraffin. 
A  similar  preparation  is  official  in  the  German  and  in  the  British 
Pharmacopoeias. 
Unguentum  Hydrargyri  Dtlutum,  Blue  Ointment,  contains  67  per 
cent,  of  unguentum  hydrargyri  and  33  per  cent,  of  petrolatum. 
Unguentum  hydrargyri  is  as  before  50  per  cent.,  therefore  the  diluted 
ointment  is  33  5  per  cent.  The  stronger  ointment  is  called  "  mercu- 
rial ointment  "  and  the  diluted  preparation  is  known  as  "  blue 
ointment." 
A  very  useful  and  satisfactory  assay  process  for  unguentum 
hydrargyri  is  official.  This  ointment  is  official  in  the  German  Phar- 
macopoeia under  the  name  of  unguentum. 
