Am.  Jour.  Pharm.) 
Feb.,  1877.  J 
Wash-Blue  and  its  Analysis. 
65 
tion  of  ferric  sulphate  or  chloride  to  an  excess  of  potassic  ferrocya- 
nide.  The  blue  precipitate  thus  formed  contains  potassium,  and  is 
soluble  in  distilled  water  as  soon  as  freed  from  adhering  mother- liquor. 
Its  formation  is  illustrated  by  the  following  equation : 
2(K4FeCy6)  +  Fe2Cl6     =    6KC1      4-  2(FeCy6K)Fe2 
potass,  ferrocyd.  +  ferric  chid.    —  potass,  chid.  -{-        sol.  blue. 
It  is  precipitated  from  its  solution  by  shaking  it  with  such  indifferent 
pulverized  substances  as  baric  sulphate,  and  the  same  effect  is  produced 
by  hard  water  and  salt  solutions,  which  qualities  render  it  unfit  for 
wash-blue. 
The  only  allied  compound  which  finds  application  as  wash-blue  is 
insoluble  in  water,  and  is  obtained  by  the  addition  of  a  solution  of  pot- 
assic ferrocyanide,  K4FeCy6+  3H20,  to  an  equal  quantity  of  copperas, 
FeS04-f-7H20,  also  dissolved,  and  subsequent  treatment  of  the  white 
precipitate  (K2Fe5C12N12)  with  a  mixture  of  nitric  and  sulphuric  acids. 
The  product  of  this  process  is  insoluble  in  water  ;  it  will,  however, 
readily  dissolve  in  solutions  of  ammonic  tartrate,  oxalic  acid  and  potas- 
sic ferro-cyanide.  Only  the  latter  two  solvents  are  of  practical  impor- 
tance. Oxalic  acid  should  be  used  in  proportion  of  about  \  of  the 
weight  of  the  dry  blue  in  order  to  dissolve  it  entirely.  Since  oxalic 
acid  is  a  poison  it  is  doubtless  preferable  to  substitute  it  by  an  equal 
amount  of  potassic  ferrocyanide,  thus  obtaining  a  perfectly  harmless 
product.  For  the  manufacture  of  blue  ink  I  should  prefer  the  latter 
solvent  already  on  account  of  its  not  corroding  steel  pens.  The  addi- 
tion of  the  potassic  ferrocyanide  is  done  best  when  the  previously 
formed  and  oxidized  precipitate  is  sufficiently  washed  and  of  the  con- 
sistency of  a  thick  pulp  (60  per  cent,  water).  The  mixture  then  is 
repeatedly  passed  through  a  mill,  dried  at  about  120°  F.,  and  ground, 
when  it  is  ready  for  sale.  100  lbs.  of  potassic  ferrocyanide  thus  yield 
80  lbs.  of  dry  blue  (almost  exactly  the  theoretical  amount),  which 
require  about  12  lbs.  of  K4FeCy63H20  to  become  soluble. 
The  pigment  thus  obtained  forms  a  light,  dark-blue  powder,  per- 
fectly soluble  in  water  ;  in  lumps  it  possesses  a  handsome  bronze  tint. 
The  color  of  the  solution  is  a  beautiful  blue-violet,  similar  to  the  shade 
obtained  by  the  action  of  ammoniacal  vapors  on  the  pure  blue  pigment. 
Sometimes,  particularly  if  precipitated  from  very  dilute  "  liquors,"  its 
solution  shows  fluorescence.  It  cannot  be  denied  that  the  cost  of  this 
blue  is  higher  than  that  of  the  one  rendered  soluble  by  oxalic  acid. 
5 
