The  optically  rotatory  power  of  organic  substances  does  not  appear  to
have  been  examined  at  temperatures  below  0°  C.  An  attempt  to  determine
the  change  which  takes  place  in  the  rotator}^  power  of  some  substances  down
to  much  lower  temperatures  is  here  recorded.
With  this  object  in  view,  solutions  of  various  optically  active  substances  in
adcohol  and  in  petroleum  ether  were  cooled  to  a  low  temperature  by  means  of
liquid  air,  and  it  was  found  that  solutions  of  a  number  of  substances  could  be
solidified  without  losing  their  transparency.
A  jacketed  polarimeter,  10  cm.  in  length,  was  made  entirely  of  metal,
and  surrounded  with  a  thick  covering  of  wooL  Experiments  were  made  to
£nd  out  how  best  to  avoid  the  deposition  of  hoar  frost  on  the  glass  plates  at
the  ends  of  the  tube.  This  caused  some  trouble,  and,  after  trying  a  number
of  devices,  it  was  found  that,  when  the  glass  plates  used  to  close,  the  ends  of
the  tube  were  about  1  cm.  thick,  and  their  outer  surfaces  were  continually
moistened  with  absolute  alcohol,  readings  could  be  taken  at  quite  low
temperatures.
