Cosset  Yellow.  Heat  a  mixture  of
10  parts  of  litharge  finely  prepared  and
1  of  sal-ammoniac  in  a  Hessian  crucible
until  it  melts ;  then  pour  the  mass  into
a  mould,  powder  the  pieces  when  cold,
and  grind  fine  in  a  color  mill.
American  Chrome-yellow.
PARTg.
/  •^  -~\

I.  II.  III.
CiystalliKed  sugar  of  lead    .    .    21  21  21

Bichromate  of  potaaaium     ..44  4

Alum 20  20  20

IleHvygpar 10  15  20

GypKuni 20

Dissolve  the  alum  in  hot  water  and
pour  the  hot  solution  into  a  tub  con-
taining the  heavy  spar  and  gypsum,
previously  passed  through  a  fine  sieve  ;
then  wash  the  whole  gradually  and
carefully  five  times.  In  the  niean while
dissolve  the  sugar  of  lead  and  bichro-
mate of  potassium  in  separate  vessels,
and  then  stir  the  chromate  solution  very
slowly  into  the  solution  of  sugar  of
lead.  When  all  is  settled,  wash  with
fresh  water,  repeating  this  3  or  ^  times.
Finally  mix  and  mingle  the  two  pre-
cipitates carefully  and  very  intimately,
wash  twice,  and  throw  the  finished  pro-
duct upon  a  filter.  It  is  customar^  to
spread  the   residue  wiHiout   pressing


ro


TECHNO-CHEMICAL  RECEIPT  BOOK.
upon  drying  boards,  to  cut  it.  when  half
dry,  into  square  pieces,  wnich,  when
entirely  dry.  fall  off  of  their  own  ac-
cord. The  boards  should  be  placed  in
a  room  secured  from  dust  and  dirt.
But  the  pigment  dried  in  this  manner
requires  polishing.  This  is  accom-
plished by  filling  a  bag  made  of  strong
ticking  about  k  with  cakes,  tying  it,
and  two  persons,  catching  hold  on
opposite  ends,  shaking  the  bag  vigor-
ously, whereby  the  cakes,  rubbing
aorainst  each  other,  acquire  a  gloss.
The  yellow  dust  falling  through  is  col-
lected and  added  to  inferior  qualities.
