Am.  Jour.  Pharm.") 
March,  1884.  J 
Soap  Manufacture  and  the  Soap  of  Commerce. 
145 
the  appearance  considerably,  and  prevents  the  soap  having  a  sticky 
consistency  on  the  exterior  of  the  bar. 
In  treating  of  the  second  part  of  my  subject,  it  may  be  well  to  pre- 
face my  remarks  with  a  brief  account  of  the  methods  by  which  I  have 
arrived  at  the  results  which  I  propose  to  state,  as  showing  the  quality  of 
the  soaps  found  in  the  market.  I  have  now  in  my  possession  upwards 
of  three  hundred  analyses  of  soap  from  different  sources,  which  have 
been  submitted  to  me  at  various  times.  In  analyzing  these  I  have 
found  the  following  processes  the  most  convenient  and  accurate. 
The  water  is  determined  by  drying  in  an  air-bath  a  weighed  portion 
of  the  soap  at  a  temperature  of  120°C.  At  this  temperature  the  soap 
swells  up  and  the  water  is  soon  expelled  without  any  loss  of  the  fatty 
matters  or  danger  of  losing  the  substance.  The  weight  is  taken  after 
ahout  three  hours,  and  subsequent  weights  are  made  at  intervals  of 
about  an  hour  until  the  weight  is  constant. 
To  obtain  the  percentage  of  fatty  acids  I  find  it  best  to  weigh  out 
about  3  grams  of  the  soap  in  a  porcelain  or  platinum  basin,  including 
in  the  weight  of  the  basin  a  small  stirring  rod  about  3  inches  long. 
The  soap  is  then  dissolved  in  a  small  quantity  of  water  in  the  basin, 
and  when  completely  dissolved,  about  5  cc.  of  dilute  sulphuric  acid  are 
added.  This  decomposes  the  soap,  setting  free  the  fatty  acids  and 
forming  sulphate  of  soda.  The  solution  is  then  gently  warmed — pre- 
ferably on  a  water-ba.th — until  the  whole  of  the  fatty  acids  have  risen. 
It  is  then  allowed  to  cool,  and  the  fatty  matter  will  usually  form  a  solid 
cake.  If  this  does  not  occur  a  weighed  quantity  of  purified  wax  must 
be  added  and  the  whole  re-melted.  When  the  cake  is  formed  it  is 
simply  moved  a  little  from  the  side,  and  the  liquid  from  below,  which 
should  contain  no  fat,  is  poured  off.  The  cake  is  re-melted  with  dis- 
tilled water  and  allowed  to  settle  as  before.  This  is  continued  until 
the  washings  are  free  from  acid.  The  cake  is  then  melted  in  a  water 
oven  and  again  allowed  to  cool,  and  the  water  which  still  adheres  is 
removed  by  gently  touching  with  filter  paper,  and  the  basin  is  again 
placed  in  the  water  oven  and  weighed  until  the  weight  is  constant. 
From  the  figures  obtained  the  percentage  of  fatty  and  resinous  acids  is 
calculated. 
The  soda  is  determined  by  adding  to  the  filtered  solution  from  a 
given  weight  of  soap  an  excess  of  standard  acid  and  titrating  back 
the  excess  of  acid  by  means  of  standard  alkali,  using  cochineal  as 
indicator. 
10 
