146 
Identifying  Fats  and  Oils. 
J Am.  Jour.  Pharm. 
X     March,  1897. 
To  prevent  as  far  as  possible  loss  of  heat  by  radiation,  Mitchell 
and  Hehner  used  Professor  Dewar's  vacuum  jacketed  tube,  which 
he  had  employed  in  his  experiments  with  liquefied  air.  It  is  a  small 
inner  tube  soldered  at  the  neck  to  a  larger  outer  tube,  from  which 
the  air  is  practically  exhausted,  leaving  almost  a  perfect  vacuum  and 
consequently  making  it  a  non-conductor  of  heat. 
The  expense  of  such  a  tube  determined  us  to  make  our  experi- 
ments with  a  cheaper  apparatus,  so  that  our  method  could  be 
applied  and  our  results  obtained  at  any  time  or  place  without  special 
apparatus. 
m 
Magnesia  and  Cotton. 
....  Magnesia. 
Fig.  1. 
The  apparatus  we  adopted  consisted  of  a  larger  beaker  (a  gradu- 
ate or  other  glass  vessel  will  do  when  a  beaker  is  not  at  hand),  with 
about  one-fourth  of  an  inch  of  calcined  magnesia  in  the  bottom,  a 
test  tube  about  7  inches  in  length,  around  the  bottom  of  which  was 
wrapped  a  small  piece  of  cotton  ;  it  was  then  put  in  the  beaker  and 
imbedded  in  alternate  layers  of  cotton  and  calcined  magnesia, 
being  packed  quite  tightly  so  that  the  tube  could  be  withdrawn  and 
replaced  at  will  without  disturbing  the  nest  so  made. 
A  Centigrade  thermometer  graduated  to  fifths  of  a  degree  com- 
pleted the  apparatus,  which,  when  ready  for  use,  presented  the 
appearance  shown  in  Fig. 
