ON  THE  VALUE  OF  DIFFERENT  KINDS  OF  SOAP.  355 
It  is  very  probable  that  the  usual  explanation  which  is  offered, 
whenever  a  soap  fails  to  fulfil  the  expectations  of  its  consumer, 
viz.  that  it  contains  too  much  water,  may  be  in  many  cases 
correct.  Admitting  this,  and  various  other  contingencies,  which 
are  of  importance  in  deciding  upon  the  value  of  a  soap,  there 
appears  to  be  another  obvious  reason  why  different  soaps  con- 
taining equal  amounts  of  water  may  still  possess  different  de- 
grees of  efficacy. 
It  is  evident  from  the  different  equivalent  weights  of  the  various 
fatty  acids,  that  the" amounts  of  caustic  alkali  taken  up  by  them 
in  the  formation  of  soap  must  be  of  unlike  magnitude. 
If  it  be  true,  that  the  detergent  power  of  soap  is  entirely  de- 
pendent upon  the  amount  of  alkali  which  it  contains,  of  course 
it  follows  that  those  soaps  which  contain  the  largest  proportion 
of  alkali — or  in  other  words,  those  containing  a  fatty  acid,  the 
equivalent  weight  of  which  is  small — must  be  the  most  effica- 
cious. 
Since  the  difference  between  the  equivalents  of  the  common 
fatty  acids  are  not  large,  these  considerations  are  perhaps  of 
little  or  no  importance  in  so  far  as  concerns  the  consumption  of 
soap  in  household  economy — the  total  amount  used  in  a  single 
family  being  but  small.  In  a  manufacturing  establishment, 
however,  where  fifty  or  a  hundred  thousand  pounds  of  soap  may 
be  used  in  the  course  of  a  year,  differences  which  cannot  be 
deemed  insignificant  must  exhibit  themselves. 
For  example,  the  equivalent  weights  of  several  soaps  (re- 
garded as  anhydrous),  in  common  use,  are  as  follows: 
Oleic  acid  (red  oil)  soap,  =  3800-95 
Palm  oil  =  3588-85 
Tallow  =r  3300-95 
Cocoa-nut  oil  =  3065-45 
Calculating  from  these  weights  how  much  of  each  of  the 
other  soaps  would  be  required  to  replace  1000  pounds  of  tallow 
soap,  the  following  quantities  will  be  found  : 
Pounds  of  Per  cent. 
1151  oleic  acid  soap,  i.e.,     15-1  more  than  tallow  soap. 
1087  palm  oil       "     i.e.,       8-7  "  u 
928  cocoa-nut  oil i.e.,  7-2  less  than  "  t« 
Differences  like  these  must  certainly  be  of  importance  in 
