250  Methods  for  Analysis  of  Castile  Soap,  {*m-3lTJtmxm' 
cent. — is  excessive,  and  should  be  very  much  reduced  in  the  new 
edition. 
Tests  for  Animal  Fats. — The  pharmoeopoeia  states  that  if  a  four 
per  cent,  alcoholic  solution  of  soap  be  allowed  to  cool  it  should  not 
gelatinize,  indicating  the  absence  of  animal  fats.  The  most  satis- 
factory method  of  carrying  out  this  test  is  to  place  the  alcohol  and 
soap  in  an  Erlenmeyer  flask  and  heat  on  a  water  bath,  employing  a 
reflux  condenser  to  prevent  evaporation.  When  solution  is  com- 
plete the  material  is  allowed  to  cool  to  room  temperature  (not  below 
20°  C). 
This  test  is  not  very  satisfactory  as  the  pharmacopoeia  allows 
36  per  cent,  of  water,  and  as  most  samples  do  not  contain  that  much 
it  is  easy  to  see  that  instead  of  a  4  per  cent,  solution  one  may  have 
almost  any  strength  depending  upon  the  quantity  of  moisture,  the 
result  being  that  the  solution  gelatinizes  and  indicates  animal  fat 
4  where  none  was  used. 
Therefore  the  pharmacopoeia  should  provide  tests  to  determine 
the  origin  of  the  fat  employed  in  making  the  soap,  such  as  deter- 
mining the  iodine  number  of  the  fatty  acids  and  their  melting  poinis. 
Separation  of  the  Fatty  Acids. — To  a  portion  of  the  soap  dis- 
solved in  water  add  an  excess  of  diluted  sulphuric  acid  and  heat  on 
a  water  bath  until  the  fatty  acids  rise  to  the  top  a  clear  layer, 
then  cool  in  ice  water  and  when  the  fatty  acids  are  solidified  pour 
off  the  water.  Repeat  this  heating  and  cooling  process  twice,  then 
filter  through  paper  wetted  with  water;  this  will  retain  the  fatty 
acids  which  after  drying  are  ready  for  the  tests. 
Iodine  Number  of  Fatty  Acids. — Determine  iodine  number  of 
fatty  acids  as  directed  by  the  pharmacopoeia  for  fats  and  oils.  The 
writer  employs  the  Hanus  method  and  as  suggested  by  him  (Drug. 
Circ,  19 10,  page  106)  this  should  be  adopted  as  the  official  method 
due  to  the  keeping  qualities  of  the  solution  and  shorter  time  re- 
quired to  make  the  determination.  Having  determined  the  iodine 
number  of  the  fatty  acid  a  reference  to  Allen's  organic  analysis 
will  indicate  the  fat  or  oil  which  was  employed  in  the  preparation 
of  the  soap. 
Melting  Point  of  Fatty  Acids. — Take  some  of  the  fatty  acids 
prepared  as  above,  gently  melt  them  and  immerse  the  bulb  of  a 
thermometer  in  them ;  in  a  few  seconds  they  will  have  congealed 
and  all  that  remains  is  to  put  the  thermometer  through  a  cork  in  an 
ounce  wide  mouth  bottle  and  then  suspend  the  bottle  and  thermom- 
