ON  THE  FUSING  AND  CONGEALING  POINT  OF  FATS.  431 
after  two  days  at  42°  ;  butter  under  the  same  circumstances  fused 
at  25®  and  31-5®  C.  respectively. 
Some  fats  become  transparent  several  degrees  above  their 
fusing  point,  like  tallow  and  suet ;  while  Japan  wax  is  perfectly 
transparent  at  42°,  but  becomes  fluid  at  53  to  54°  C. 
The  tubes  with  a  thermometer  are  placed  in  a  beaker  glass, 
the  bottom  of  which  is  covered  with  several  layers  of  paper  ; 
water  is  then  poured  in  until  it  reaches  half  an  inch  above  the 
surface  of  the  fat ;  the  apparatus  is  then  placed  upon  a  piece  of 
sheet  iron  and  very  slowly  heated  by  an  alcohol  lamp,  until  the 
liquified  fat  is  pushed  up  to  the  level  of  the  surrounding  water 
by  the  water  entering  at  the  lower  orifice  of  the  tubes.  A  few 
fats  rise  so  slowly  in  the  tubes  that  the  temperature  still  per- 
ceptibly  increases  j  the  difference,  however,  rarely  reaches  half 
a  degree. 
All  true  fats,  that  is  compounds  of  oxide  of  glyceryle,  congeal 
more  or  less  below  their  fusing  point,  while,  for  instance,  wax  and 
spermaceti  congeal  immediately  below  the  temperature  at  which 
they  fuse.  On  congealing  the  true  fats  always  show  an  eleva- 
tion of  temperature  sometimes  to  near  the  fusing  point. 
The  author's  experiments  have  given  the  following  results : 
Fats. 
Fuse  at 
Congeal  at 
Temp,  rises  to 
Beef  tallow,  fresh, 
430  c. 
33»  C. 
36— 37<^  C. 
older, 
43-5 
34 
38 
Mutton  suet,  fresh, 
47 
36 
40—41 
old, 
60-5 
39-5 
44—45 
Hog's  lard, 
41-5—42 
30 
32 
Butter,  fresh. 
31—31-5 
19—20 
19-5— 20-6 
tub, 
32-5 
24 
25-5 
Japan  wax. 
40-5—41 
45-5—46 
Cacao  butter, 
33-5—34 
20-5 
22—23 
Palm  oil,  fresh,  soft, 
30 
21 
21-5 
fresh,  harder. 
38 
24 
25 
old. 
42 
38 
39-5 
Oil  of  Mace, 
43.6_44 
33 
41-6—42 
Beeswax,  yellow, 
62-62-5 
1  Congeal  just  below  the  fusing 
"  white, 
63—63-5 
)■  point,  without 
rise  of  temper- 
Spermaceti, 
44_44.5 
J  ture. 
Wittsteins  Viertlj.  Schr,  1869,  272-278,  from  Poggendorff's 
AnnaleUf  cxxxiii,  121. 
