144       Soap  Manufacture  and  the  Soap  of  Commerce.     {AmMa™h  Ji™' 
is  produced  generally  by  the  addition  of  ultramarine,  which  gives  to 
the  soap  a  bright  appearance. 
Some  samples,  sold  at  low  prices,  have  come  under  my  notice  which 
have  not  only  been  run  with  silicate  but  contain  from  6  to  8  per  cent, 
of  common  salt  and  not  more  than  one  quarter  of  their  weight  of  fatty 
acids.  The  salt  is  of  no  value  as  a  detergent  agent,  and  must  be  looked 
upon  simply  as  a  "  make  weight."  It  is  only  with  soaps  made  from 
palm  nut  and  cocoa  nut  oil  that  the  salt  will  combine  properly.  The 
peculiar  behavior  of  these  two  soaps  in  salt  water  renders  them  valu- 
able for  marine  purposes.  Very  considerable  experience  is  required  in 
making  a  soap  of  low  quality  which  shall  be  firm  to  the  touch  and 
present  the  appearances  of  a  good  soap,  and  the  difficulty  is  increased 
in  the  case  of  common  mottled  soap,  where  it  is  necessary  to  have  the 
mottling  equally  distributed  throughout  the  mass.  The  methods  by 
by  which  this  is  attained  are  kept,  as  a  rule,  as  trade  secrets,  but  no 
great  difficulty  is  experienced  when  the  matter  is  approached  on  scien- 
tific principles. 
In  the  common  soaps  which  are  usually  used  for  scouring,  etc.,  the 
proportion  of  soda  in  excess  of  the  fatty  acids  may  be  greater  than  in 
those  used  for  finer  purposes  or  for  toilet  use.  The  choice  of  the  fat 
must  also  be  regulated  by  the  purposes  to  which  the  soap  is  intended 
to  be  put. 
The  details  of  the  manufacture  require  careful  attention,  and  can 
only  be  mastered  after  long  experience,  but  it  is  necessary  that  all  the 
processes  should  be  carried  on  in  the  lines  I  have  indicated.  The 
peculiar  behavior  of  each  kind  of  soap  would  occupy  more  time  than 
is  at  my  disposal,  nor  would  it  serve  to  elucidate  the  processes  ;  but  it 
is  important  that  the  manufacturer  should  be  conversant  with  their 
properties.  As  a  rule,  the  larger  the  amount  of  stearin  or  palmitin 
there  is  in  the  fat  operated  upon  the  harder  will  be  the  soap. 
Before  closing  the  remarks  upon  the  manufacture  I  may  just  refer 
to  two  methods  which  are  occasionally  resorted  to,  to  improve  the 
appearance  of  common  soaps.  The  first  of  these  consists  in  placing 
the  soap  in  an  oven  or  stove,  so  that  it  may  become  surface  died 
and  present  a  hard  "  skin."  The  second  of  these  consists  in  dipping 
the  soap  in  a  strong  solution  of  brine  or  other  liquid.  The  salt  has  a 
great  affinity  for  water  and  removes  it  from  the  surface  of  the  soap? 
but  the  soap  itself  is  quite  insoluble.    This  process  improves  the 
