2IO 
Volumetric  Solutions  of  U.S. P. 
Am.  Jour.  Pbarm 
May,  1910. 
The  funnel  is  then  washed  and  the  washings  added  to  the  main  solu- 
tion. This  solution  is  then  titrated  with  a  thiocyanate  solution  of 
about  j-q  strength,  using  ferric  alum  as  indicator,  thus  determining 
the  exact  value  of  the  thiocyanate  solution.  By  means  of  this  thio- 
cyanate solution,  a  tenth-normal  silver  nitrate  solution  is  prepared  ; 
and  the  latter  is  then  used  in  preparing  -f^  HC1.  By  means  of  this 
HCl.y-o  alkali  is  prepared ;  and  by  means  of  the  latter,  an  oxalic  acid 
solution  is  standardized.  The  latter  is  then  used  in  standardizing  the 
permanganate  solution  ;  and  by  means  of  the  permanganate  solution, 
Yo  sodium  thiosulphate  is  prepared,  the  process  being  essentially 
the  same  as  that  given  in  the  U.S. P.,  only  substituting  the  per- 
manganate in  place  of  the  dichromate ;  the  reason  for  choosing  the 
KMn04  for  this  purpose,  instead  of  the  dichromate,  being  that  a 
sharper  end  reaction  may  be  obtained  and,  as  pointed  out  by 
Bruhns,23  the  former  has  also  the  advantage  in  that  the  reaction 
is  practically  instantaneous.  This,  therefore,  would  give  us  all 
the  necessary  solutions  on  which  is  based  the  entire  system  of 
volumetric  analysis  as  usually  carried  out. 
In  this  connection  it  is  also  interesting  to  note  that  Rothmund 
and  Burgstaller 24  have  recently  shown  that  in  shaking  the  AgCl 
suspension  with  ether,  in  determining  chlorides  by  means  of  the  Yol- 
hard  thiocyanate  method,  nitration  of  the  AgCl  is  rendered  unneces- 
sary, and  accurate  results  are  obtained  by  direct  titration  of  the 
unfiltered  mixture  even  when  the  amounts  of  chlorine  are  small. 
And  as  further  showing  the  advantages  of  metallic  silver  as  the 
standard  in  volumetric  analysis,  we  may  mention  the  recent  work 
of  Gooch  and  Perkins,25  who  showed  that  free  iodine  in  solution 
may  be  accurately  determined  through  its  reaction  with  metallic 
silver.  Likewise,  Hopfgartner  20  has  shown  that  potassium  perman- 
ganate may  be  standardized  directly  by  means  of  metallic  silver  by 
dissolving  the  latter  in  ferric  ammonium  sulphate  which  has  been 
acidified  with  sulphuric  acid  and  titrating  the  ferrous  salt  thus 
formed  with  the  permanganate  solution.  Finally,  when  we  recall 
the  present  commendable  tendency  to  refer  all  important  work  to 
exact  standards,  as  may  be  illustrated  by  the  work  of  the  Hygienic 
Laboratory  in  furnishing  the  standard  for  the  preparation  of  the 
23  Jour.  Chew.  Soc,  go,  ii,  577  (1906). 
24  Zcit.  anorg.  Chem.,  63,  330-6  (1909). 
25  Ibid.,  318-324. 
26 Jour.  Chem.  Soc,  88,  ii,  484  (1905). 
