Augusrig™: }        U.  S.  Pharmacopoeial  Revision.  553 
salts  has  proved  very  satisfactory.  It  is  recommended  that  this  be 
extended  to  other  assays  which  are  frequently  used  in  the  U.  S.  P.,  such 
as  tests  for  acids,  ferric  salts,  zinc  salts,  benzoates,  and  salicylates. 
It  is  further  suggested  that  wherever  such  assays  are  available 
and  are  not  unduly  laborious,  the  active  principle  of  the  substances 
be  determined.  In  calcium  chloride  the  calcium  should  be  estimated 
and  in  sodium  benzoate  and  salicylate  the  respective  acid  determined. 
The  correctness  of  this  recommendation  is  self-evident. 
Test  for  Zinc. — The  U.  S.  P.  test  for  heavy  metals  takes  no 
cognizance  of  zinc.  Although  contamination  of  U.  S.  P.  products 
with  this  metal  is  not  of  frequent  occurrence,  it  is  desirable  to  make 
provision  against  its  presence  in  undue  proportions.  It  is  there- 
fore recommended  that  a  test  for  zinc  be  included  in  the  heavy 
metals  test. 
Drying  to  Constant  Weight. — It  is  highly  desirable  that  this  ex- 
pression, so  frequently  used  in  the  Pharmacopoeia,  be  defined. 
A  definition  of  this  term  will  be  of  particular  value  in  the  determina- 
tion of  water  in  soaps  and  other  products  of  similar  character.  It 
is  impossible  to  strictly  dry  soap  to  constant  weight.  After  the 
water  has  been  presumably  expelled,  soap  will  keep  on  losing  in 
weight  to  a  small  extent  on  further  drying,  and  occasionally  a  gain 
in  weight  has  also  been  noted.  A  definition  along  the  following 
lines  might  answer.  The  expression  ''dried  to  constant  weight''  is 
intended  to  mean  that  two  consecutive  weighings,  after  drying  for 
an  additional  hour,  do  not  differ  by  more  than  o.  i  per  cent. 
Unweighahle. — It  is  recommended  that  the  term  "negligible" 
be  used  instead  of  "unweighable,"  retaining  for  it  the  same  definition 
as  is  now  used  for  unweighable. 
Test  Solutions. — The  majority  of  U.  S.  P.  test  solutions  are  made 
up  to  10  per  cent,  regardless  of  whether  the  substance  is  anhydrous 
or  contains  60  per  cent,  of  water.  The  solutions  bear  no  relation 
to  each  other.  This  is  not  in  keeping  with  good  scientific  practice. 
It  will  suffice  to  note  that  whereas  diluted  hydrochloric  acid  is 
nearly  triple  normal,  diluted  nitric  acid  is  1V2  normal  and  diluted 
sulphuric  acid  is  double  normal.  It  is  recommended  that  in  the 
next  revision  test  solutions  be  prepared  on  the  normality  basis. 
The  advantages  of  this  system  are  very  obvious.  As  a  matter  of 
fact,  this  is  not  an  innovation.  vSeveral  of  the  test  solutions  now 
official — silver  nitrate  T.  S.,  potassium  permanganate  T.  S.,  sulpho- 
cyanate,  and  sodium  thiosulphate,  are  made  up  on  normality  basis. 
