PROCESS  FOR  DETERMINING  THE  VALUE   OF  SOAP. 
235 
sent  in  a  soap  in  considerable  quantity,  without  in  an  equal  degree 
influencing  the  exterior  appearance,  hardness,  &c.  The  means 
of  determining  the  per-centage  of  dry  substance  are, —  1st,  drying  a 
weighed  quantity  in  a  water-bath ;  and  2nd,  salting  out,  or  intro- 
ducing the  soap  into  a  saturated  solution  of  chloride  of  sodium  and 
boiling,  by  which  means  it  concretes  together  into  a  solid  mass 
tolerably  free  from  water.  With  regard  to  the  first  method,  many 
have  no  doubt  found  that  when  the  soap  has  been  heated  for  a  long 
time  in  the  water-bath,  and  has  commenced  to  melt,  it  not  only 
does  not  give  off  any  more  water,  but  becomes  very  hygroscopic, 
and  attracts  moisture  again  very  rapidly. 
Old  Marseilles  soap,  exposed  to  a  temperature  of  86°  F.  for  six 
hours,  was  found  to  have  lost  3*2  per  cent.,  and  when  kept  at 
212°  F.  for  two  hours,  there  was  no  further  diminution  in  weight ; 
after  exposure  to  the  air  for  a  few  hours,  it  weighed  1  per  cent, 
more  than  at  first.  Several  other  specimens  showed  that  soap, 
when  heated  to  212°  F.,  increased  in  weight  during  the  weighing. 
If  such  experiments  were  carried  out  by  inexperienced  persons,  er- 
rors would  be  the  natural  consequence.  The  process  of  salting  out 
may  be  applicable  upon  a  somewhat  large  scale,  with,  for  exam- 
ple, a  pound  of  soap,  and  is  then  better  adapted  than  the  other  to  give 
trustworthy  indication  of  the  per-centage  of  actual  soap.  But  the 
determination  of  dry  soap  has  no  bearing  upon  the  very  important 
question  of  the  possible  presence  of  adulterating  substances,  still 
less  upon  the  second  and  third  points  mentioned  above. 
It  is  by  no  means  difficult  to  determine  the  quantity  of  alkali  and 
that  of  fat  in  a  soap;  but  the  operation  is  far  more  tedious  and 
troublesome  when  it  is  at  the  same  time  requisite  to  ascertain  whe- 
ther the  soap  contains  free  alkali  or  fat,  and  the  proportion  of  one 
or  other  to  the  fat  and  alkali  in  combination.  Nevertheless  this 
question  may  not  generally  be  of  great  consequence,  as  both  errors 
would  scarcely  be  owing  to  a  fraudulent  intention,  and  their  mag- 
nitude would  be  confined  within  a  narrow  limit.  The  uncombined 
alkali  in  hard  (soda)  soap  may  be  determined  by  exposing  the  soap 
in  fine  shavings  to  the  air,  so  that  the  alkali  may  absorb  carbonic 
acid,  treating  it  with  strong  alcohol,  and  examining  the  insoluble 
residue,  which  may  contain  other  salts  or  insoluble  substances,  for 
alkali.  A  process  recommended  by  Stockhardt  is  less  troublesome  ; 
it  consists  in  adding  to  a  hot  concentrated  solution  of  soap,  bitar- 
