398  The  Preparation  of  Sapo  Viridis.      { AmAJu°gu.^ ^rm' 
up  to  the  standard  requiring  5*8  and  5'84  per  cent,  of  hydrate  of  potash. 
Boil  quietly  and  stir  frequently  until  the  mass  becomes  clear,  which, 
with  4  ounces  of  oil  and  12  fluidounces  of  liquor,  will  require  about 
one  hour,  and  with  10  pounds  of  oil  about  five  hours.  If,  during  the 
process,  the  mass  becomes  too  thick  to  stir  easily,  add  a  little  water. 
Allow  the  soap  to  become  cool,  but  before  it  sets  work  in  the  coloring 
matter,  which  must  be  previously  prepared  by  boiling  finely  powdered 
indigo  with  water  until  the  color  is  formed  into  a  thin  paste.  Twenty 
grains  of  indigo,  boiled  with  ij  ounce  of  water  until  the  mixture  is 
reduced  to  about  1  drachm,  will  answer  for  the  soap  from  4  ounces  of 
oil.  The  soap  must  not  be  too  hot,  nor  must  it  be  reboiled  after  add- 
ing the  coloring,  or  the  green  will  be  destroyed.  Mr.  Betz's  state- 
ment, that  nothing  answers  so  well  as  "the  green  coloring  matter  pre- 
cipitated from  a  solution  of  indigo  by  lime,"  is,  to  say  the  least  of  it, 
very  vague.  The  method  I  have  given  is  that  pursued  by  continental 
makers  of  green  soap,1  and  works  well.  A  Berlin-ware  or  Wedge- 
wood  dish  may,  of  course,  be  used  instead  of  iron  or  copper,  but  as  the 
boiling  point  of  the  mixture  is  high  there  is  great  liability  of  fracture, 
and  cold  water  must  be  added  very  cautiously,  and  the  stirring  must  be 
almost  continuous. 
The  proportions  of  oil  and  alkali  given  above  are  such  as  will  turn 
out  a  satisfactory  article  with  most  samples  of  linseed  oil,  and  with  lye 
of  the  proper  strength.  I  think  these  definite  directions  regarding 
quantities  advisable  for  those  who  have  not  had  much  experience  in 
saponification.  The  best  guide  in  soap-making,  where  the  strength  of 
the  lye  is  not  known,  is  that  afforded  by  applying  a  very  small  portion 
of  the  soap  to  the  tip  of  the  tongue.  The  sharp  taste  of  the  alkali 
indicates  more  boiling  or  more  oil,  or  perhaps  more  water.  This  test, 
though  not  very  scientific,  is  eminently  practical,  and  is  very  generally 
employed. 
The  product  will  be  about  twice  the  weight  of  the  oil  used,  and 
should  be  of  a  dull  bottle-green  color,  and  in  consistence  at  least  not 
thicker  than  lard  or  butter  at  moderate  temperatures,  just  so  that  it  will 
retain  its  form  and  might  be  carried  on  paper. 
Genuine  green  soap  should  be  made  from  hempseed  oil,  and  is  largely 
used  in  France  (savon  vert),  Germany  (grilne  Seife)  and  other  conti- 
nental countries,  where  it  is  almost  universally  employed  in  the  house- 
1 "  lire's  Dictionary,"  vol.  ii,  p.  699. 
