460  Gleanings  from  the  German  Journals.  {Am'sijt.?i892arm* 
the  fats  and  oils  and  then  by  warming  cause  these  to  react  with 
yellow  oxide  of  mercury  ;  the  products  were  entirely  satisfactory 
for  medicinal  use.  The  fats  were  saponified  in  the  usual  manner  and 
the  fatty  acids  liberated  from  the  alkali-soaps  by  adding  hydro- 
chloric acid;  after  boiling  the  fatty  acids  with  several  portions  of 
water  to  remove  mineral  acid,  they  are  transferred  to  a  capsule  and 
dried  in  an  air-bath.  To  determine  the  necessary  mercuric  oxide 
about  two  grams  of  the  acid  are  titrated  with  ~  alkali,  using  phenol- 
phthalein  as  indicator  (for  most  purposes  the  oxide  necessary  can  be 
calculated  if  the  average  molecular  weight  of  the  fatty  acids  is 
known,  this  requiring  108  parts  mercuric  oxide).  The  acids  and 
oxide  are  rubbed  together ;  then  a  little  water  added  and  heated 
carefully  on  a  water-bath  until  the  color  of  the  oxide  disappears  (if 
the  acids  separated  from  tallow  be  used  the  operation  must  be  com- 
pleted by  finally  heating  carefully  on  an  oil-bath) ;  to  obtain  good 
results  excessive  heating  must  be  avoided.  The  following  table 
gives  (1)  the  source,  (2)  saponification-equivalent,  (3)  average  molecu- 
lar weight,  and (4)  iodine  absorption  of  the  fatty  acids;  (5) percentage 
of  HgO,  (6)  color,  and  (7)  consistence  of  the  resulting  soaps. 
I 
2 
3 
4 
5 
6 
7 
Sesame  oil,    .  .  . 
198-0 
283-3 
no'5 
28-26 
yellowish 
of  cold  cream 
Olive  oil,  .... 
200  •  3 
280-1 
88-5 
28-48 
yellow 
<( 
Lard,  
20  2 'O 
277-8 
65-0 
28-69 
almost  white 
firmer 
Palm  oil,  .... 
207-0 
271-0 
534 
29-18 
orange  to  brown 
Beef  suet,  .... 
200  *o 
280-5 
38'5 
28-45 
almost  white 
of  lead  plaster 
Cocoanut  oil,    .  . 
276-3 
205-3 
8-6 
357o 
waxy 
Stearic  acid,  .  .  . 
205-7 
272-7 
17 
29-05 
<  < 
friable 
The  consistency  of  the  soaps,  also  their  susceptibility  to  decompo- 
sition by  heat,  follow  the  variation  in  the  iodine-absorption  of  the 
fatty  acids ;  while  the  soap  made  from  sesame  oil-acids  is  soft  so 
that  it  can  be  drawn  into  threads,  it  is  most  easily  decomposed  by 
heat ;  commercial  stearic  acid  yields  a  soap  so  hard  that  it  can  be 
powdered  and  used  in  this  condition.  These  soaps  are  much  more 
permanent  than  the  commercial  oleates  (solution  of  true  oleate  in 
excess  of  oleic  acid) ;  for  the  preparation  of  pastes  and  ointments 
the  soap  made  from  olive  oil  is  most  desirable,  while  for  plasters  the 
soaps  from  beef  suet  or  cocoanut  oil,  owing  to  their  firmer  con- 
