420  DETERMINATION  OF  TALLOW  OR  STEARIC  ACID  IN  WAX. 
with  cold  distilled  water,  as  long  as  the  washings  become  brown, 
by  the  addition  of  sulphuretted  hydrogen  water.  Then  place 
the  residue  in  a  small  porcelain  capsule,  and  weigh  it  again, 
after  having  perfectly  dried  it  in  a  temperature  of  212°  Fahr. 
If  the  wax  is  pure,  one  dram  of  the  original  precipitate  will 
have  been  reduced  to  one-half  two-thirds  grain.  If  ten  per  cent, 
of  tallow  were  mixed  with  it,  the  precipitate  will  now  weigh  two 
to  two-and-half  grains.  If  twenty  per  cent,  tallow,  it  will  be 
three  three-fourths  to  four  one-fourth  grains. 
Unfortunately,  the  quantity  of  the  precipitate  is  not  constant, 
even  with  the  utmost  care.  The  quantitative  adulteration  of 
wax  by  stearic  acid  is  more  easily  detected ;  for  one  dram  of 
wax,  adulterated  with  five  per  cent,  of  stearic  acid,  gives,  when 
treated  in  the  above  manner,  2  to  2§  grains  of  precipitate  ;  with 
ten  per  cent.,  4  to  4|  grains;  with  twenty  per  cent.,  eight  to 
nine  grains.  The  yellow  wax  does  not  materially  differ  in  this 
respect  from  white  wax,  and  its  adulteration  can  be  detected  in 
the  same  way. 
POSTSCRIPT  BY  DR.  BUCHNER. 
The  author  of  the  foregoing  prize  essay  has  accompanied  his 
brochure  with  ten  samples  of  wax. — 1,  perfectly  pure  white  wax  ; 
2,  white  wax  adulterated  with  two  and-a-half,  five,  ten,  twenty, 
thirty  and  fifty  per  cent,  stearic  acid  ;  3,  white  wax  adulterated 
with  five,  ten  and  twenty  per  cent,  of  tallow.  The  judges  have 
come  to  the  conviction  that  these  adulterations  could  only  ap- 
proximately be  discovered  by  an  exact  comparison  of  the  melting 
degree,  and  of  the  specific  weight,  if  the  chemical  test  of  My. 
Geith  was  not  made  use  of.  The  sensible  properties,  smell, 
color,  brilliancy,  transparency,  softness,  toughness,  fracture  and 
texture,  are  not  safe  indications  for  an  adulteration,  and  al- 
though wax,  mixed  with  equal  proportions  of  stearic  acid,  is,  in 
a  cold  state,  considerable  more  brittle  and  less  soft  and  pliable 
than  pure  wax,  still  this  difference  is,  in  an  adulteration  with 
twenty  to  thirty  per  cent,  of  tallow  or  stearic  acid,  not  great 
enough,  as  to  discover  with  certainty  the  degree  of  adultera- 
tion. 
M.  Lepage,  of  Gisors,  has  compared  the  different  melting 
points  of  pure  bees-wax  and  of  tallow,  and  also  of  given  mix- 
