66  Wash-Blue  and  its  Analysis.  {^'fIIT^T™' 
The  "patent"  boxes,  however,  it  is  sold  in  contain  such  homoeopathic 
quantities  (average  60  grains,  sold  at  ten  cents)  that  the  cost  of  package 
and  label  far  surpasses  that  of  the  contents,  still  leaving  a  fair  profit  to 
the  wholesale  manufacturer. 
The  greater  number  of  the  "  wash-blues  "  in  the  market  contain 
oxalic  acid,  the  detection  of  which  is  by  no  means  so  easy  a  matter  as 
might  be  imagined.  It  is  evident  that  on  addition  of  calcic  acetate  not 
only  calcic  oxalate  will  precipitate,  but  also  the  Berlin  blue,  which  thus 
becomes  deprived  of  its  solvent.  The  non-transparency  of  the  solu- 
tion (except  on  excessive  dilution)  neither  facilitates  a  direct  reaction. 
The  method  which  I  would  propose,  and  which  has  given  very  satis- 
factory results,  as  well  for  the  qualitative  detection  as  for  the  estima- 
tion of  oxalic  acid,  in  this  case  is  as  follows : 
About  10  grains  of  the  blue  to  be  tested- are  heated  with  caustic 
soda.  The  pigment  thus  becomes  converted  into  sodic  ferrocyanide 
and  hydrated  ferric  oxide,  while  the  oxalic  acid  will  form  sodic  oxalate. 
The  iron  is  filtered  off  and  the  filtrate  acidified  with  dilute  acetic  acid. 
If  oxalic  acid  is  present,  calcic  oxalate  at  once  will  precipitate  on  addi- 
tion of  calcic  acetate.  As  all  the  circumstances  for  the  formation  of 
ferric  or  a  basic  oxalate  are  present,  it  is  advisable  to  dissolve  the  ferric 
precipitate  in  a  few  drops  of  hydrochloric  acid  ;  add  sodic  acetate  and 
acetic  acid  to  the  cold  solution,  which,  although  assuming  a  red  color, 
will  not  form  a  precipitate  of  basic  acetate  of  iron  except  on  boiling.  On 
addition  of  calcic  acetate  the  oxalic  acid  can  be  recognized  by  the  pre- 
cipitation of  calcic  oxalate,  and  it  may  be  estimated  in  the  usual  manner 
if  a  quantitative  determination  should  be  desired.  Although  I  have  never 
found  oxalic  acid  in  this  ferric  precipitate,  I  would  recommend  not  to 
omit  testing  for  it. 
As  to  the  detection  of  potassic  ferrocyanide  in  wash-blue,  I  have 
seen  the  following  test  applied,  viz.  :  A  few  drops  ot  the  concentrated 
blue  solution  are  dropped  on  a  piece  of  filtering-paper  and  allowed  to 
spread.  Owing  to  the  capillarity,  around  the  blue  spot  a  colorless  wet 
zone  will  form,  which,  although  being  hardly  of  the  breadth  of  TVth 
of  an  inch,  will  allow  the  detection  of  potassic  ferrocyanide  on  adding 
to  it  a  drop  of  a  dilute  solution  of  ferric  chloride  by  means  of  a  thin 
glass  rod  (formation  of  Berlin  blue). 
For  confirmation  I  should  recommend  the  following  tests  : 
If  potassic  ferrocyanide  is  contained  in  a  wash-blue,  the  aqueous 
extract  of  its  residue  on  ignition  will  contain  potassic  cyanide  (silver 
