THE 
AMERICAN  JOURNAL  OF  PHARMACY. 
AUGUST,    187  4. 
A  PROCESS  FOR  THE  ANALYSIS  OP  SOAP,  BASED  IN  PART 
ON  THAT  OF  MO.FF1T. 
By  A  Sienikr,  Jr. 
I.  Substances  to  be  Sought. 
Three  essential  constituents  are  found  in  all  soaps,  viz.,  a  base,  a 
fatty  acid  and  water.  Besides  these,  there  is  usually  more  or  less 
glycerin,  sometimes  added  intentionally,  though  generally  due  to  im- 
perfect separation  ;  an  excess  of  alkali  and  alkaline  and  earthy  car- 
bonates are  commonly  found,  and  sulphates  and  chlorides  are  of  fre- 
quent occurrence.  By  the  following  method  the  fatty  acids,  save 
resin,  are  estimated  together.  The  base  is  estimated  as  soda  in  the 
case  of  hard  soaps,  and  as  potash  in  that  of  soft.  The  water  is  deter- 
mined by  subtracting  the  weight  of  all  the  substances  found  from 
the  gross  weight  (it  should  not  exceed  20  or  30  per  cent). 
Recapitulating,  the  substances  to  be  sought  are 
Alkali,  combined  and  free,  Carbonate, 
Fatty  acids  (their  fusing  point  Resin, 
to  be  found),  Salts  and  coloring  matter, 
Glycerin,  Water. 
II.  Process. 
a.  Average  the  soap  fairly,  and  weigh  out  three  portions— ten 
grams,  ten  grams  and  forty  grams. 
b.  Digest  ten  grams  with  alcohol  (five  or  six  ounces),  heat  over 
water  bath,  filter,  wash  the  residue  frequently  with  hot  alcohol  (the 
funnel  being  kept  hot  by  apparatus  for  hot  filtration).  Treat  residue 
as  (1),  and  filtrate  as  (2). 
(1).  Residue.    (Carbonates,  other  salts,  coloring  matter,  &c.) 
Dry  in  oven  at  212°  F.    (Counterpoise  filter)  and  weigh.  Digest 
2 
