Am.  Jour.  Pharm.  ) 
April,  1878.  J 
Paints,  Colors  and  their  Analysis, 
lS3 
state  that  these  mixtures  are  obtained  by  precipitation,  so  that  the  yellow 
and  blue  pigments  meet  in  statu  nascendi.  For  instance,  into  a  large 
vessel  containing  a  solution  of  blue  in  oxalic  acid,  lead  nitrate  or  acetate 
is  run  in  at  one  and  potassic  bichromate  at  the  other  extremity,  while 
the  contents  of  the  vessel  are  constantly  agitated.  The  lime  contained 
in  the  large  quantities  of  water  used  as  solvents  suffices  to  deprive  the 
blue  of  its  relatively  small  quantity  of  solvent,  forming  calcic  oxalate.1 
In  this  case  the  use  of  oxalic  acid  is  fully  justified.  Far  more  frequently, 
however,  the  blue  is  applied  as  a  thin  pulp,  not  dissolved  in  oxalic  acid, 
which  process,  besides  being  cheaper,  answers  equally  well.  Clay, 
gypsum  and  barytes,  or  whatever  white  admixture  is  desired,  are  added 
to  the  green  pulp  with  constant  stirring,  and  more  thoroughly  incor- 
porated by  subsequent  repeated  grinding.  Various  other  methods, 
though  chiefly  based  on  the  above  principles,  are  in  use  at  the  different 
works  to  produce  different  qualities  and  shades  of  chrome-greens.  The 
following  analyses  may  illustrate  the  composition  of  this  class  of  paints: 
Shade — Light-green,  similar  to  Paris-green,  but  less  fiery  : 
Moisture,          ....  0-4500  per  cent. 
Loss  on  ignition,       .              .              .  31750 
f  Baric  sulphate,                .              .              .  61-2200 
{  Gypsum,                  .              .              .  0*1290 
Plumbic  sulphate,            .              .              .  5*0000 
Zinc  oxide,          •                   .              .  0*5750 
\  Alumina,          ....  4  0500 
!  Magnesia,  ....  0-2736 
j  Lime,                ....  0*5000 
[  Silicic  acid,               .              .              .  11-2400 
(  Plumbic  oxide,  ....  7*4700 
{  Chromic  acid,           .              .              .3  3400 
Ferric  oxide,     ....  2  8000 
h. 
d. 
100*2226 
a  =  barytes  ;  b  —  China-clay  ;  c  =  chrome-yellow  ;  d  =  non-vola- 
tile portion,  namely,  ferric  oxide  of  the  blue,  which  is  equal  to  half  the 
quantity  of  pure  u  commercial"  blue  present  (see  "  Wash-blue  and  its 
Analysis,"  vol.  49,  1877,  P-  67,  °f  this  journal).  The  practical  work- 
ing formula,  derived  from  this  analysis,  is  as  follows:  Prussian-blue, 
5*5;  chrome-yellow,  II'O;  barytes,  62*0;  China-clay,  i6'0,  and 
plumbic  sulphate,  5-5  parts — total,  100.  This  green  also  contained 
small  quantities  of  tartaric  and  oxalic  acids. 
'An  oxalic  solution  of  Prussian-blue  easily  throws  down  the  pigment  when  other 
precipitates  are  produced  in  it,  as  in  this  case,  even  without  presence  of  lime  or  other 
similarly  acting  agent. 
