DETERMINATION  OP  TALLOW  OR  STEARIC  ACID  IN  WAX.  421 
tures  of  these  two  substances,  and  has  found  that  it  is  possible, 
by  means  of  this  physical  test,  to  discover  with  certainty  the 
purity  or  adulteration  of  wax.  M.  Legrip,  of  Chambon,  has 
closely  examined  this  wax  test  of  Lepage,  and  found  it  perfectly 
correct  and  safe,  as  far  as  no  great  exactness  with  regard  to  the 
quantity  of  the  admixed  tallow  is  required.*  This  method  has 
this  advantage — that  it  is  easily  performed,  not  expensive,  and 
causes  no  great  waste  of  wax.  It  is  done  in  the  following  man- 
ner : 
In  a  quantity  of  melted  wax  the  bulb  of  a  thermometer  is 
immersed,  so  that  it  is  covered  with  a  moderately  thick  coat  of 
wax,  and  when  perfectly  cold,  the  thermometer  is  fastened  with 
a  cork  into  a  retort  with  a  long  neck,  so  that  the  bulb  of  the 
thermometer  is  suspended  in  the  body  of  the  retort.  The  latter 
is  then  placed  in  a  vessel  filled  with  water,  which  is  slowly 
heated  over  a  moderate  fire,  the  globe  and  the  scale  being  closely 
watched.  As  soon  as  the  wax  begins  to  melt  and  to  drip  off, 
the  degree  of  temperature  is  marked  down  and  composed  with 
the  following  scale,  given  by  Lepage  and  Legrip  : 
Pure  tallow  melts  at  46°  0. 
A  mixture  of  19  parts  of  tallow,  and  1  of  white  wax,  at  47.0  C. 
"  7    "  "  1  "  49.5  C. 
"  5    "  «  1  "  52.5  C. 
"  3    "  "  1  «  55.5  C. 
"  1    "  "  1  "  59.0  C. 
«•  1    "  «  3  "  60.5  0. 
"  1    "  "  5  "  61.5  C. 
"  1    "  "  7  "  62.5  C. 
«  1    «  «  11  "  63.0  C. 
"  1    "  "  19  "  64.0  C. 
Pure  white  wax  *  64.0  C. 
Pure  yellow  wax  ,  64.0  C. 
The  difference  between  the  melting  point  of  wax  and  that  of 
tallow  is,  therefore,  18°,  which  gives  sufficient  scope  for  com- 
parison ;  still  the  melting  point  of  a  mixture  of  given  parts  of 
wax  and  tallow,  cannot  be  determined  by  calculation,  if  the 
melting  points  of  wax  and  tallow  alone  are  given  ;  for,  accord- 
ing to  theory,  a  mixture  of  fifty  parts  of  wax  and  fifty  parts  of 
tallow,  should  melt  at  55°  C.  as  =55,  but  experimentally 
it  was  found  to  be  at  59Q  C ;  we  must,  moreover,  observe  here, 
*  Jour.  de.  Chim.  Med.,  1845,  p.  34. 
