AmjSe,riS7arm'}        Oil  of  Erigeron  and  Fireweed.  305 
of  Pharmacy)  ;  the  temperatures  for  sp.  gr.  and  boiling  points  were 
taken  by  a  thermometer  specially  treated  at  Yale  Observatory1. 
NATUKAL  OIL  OF  ERIGERON. 
No.  Sp.  Gr.  at  15°  C.  59°  F.  Polarizing  Angle. 
1  
2  
3  
4  
5  
"870  (resinous.) 
—60° 
•864 
—51 
•856 
—23 
•865 
—58 
•864 
—51 
•861 
—30 
•864 
—47'5 
•865 
—57 
>909 
377-5 
Dividing  totals  by  8  gives  average  polarization  of  — 47'19,  and  sp.  gr.  *8636. 
Having  five  samples  of  the  oil  of  fireweed  of  my  own  distillation, 
they  were  submitted  to  like  tests  at  the  same  temperature,  with  the 
following  results  : 
No.  Sp.  Gr.  Polarizing  Angle. 
1  -858  —  4 
2  -854  —  35 
3  -847  +355 
4  -905  (resinous)  +  33 
'    5  -907  +44 
Totals,       .       4*366  +110. 
Dividing  by  5  gives  average  polarization  of  +  22  and  Sp.  Gr.  -8732. 
It  will  be  noticed  that  the  fireweed  polarizes  with  wider  variations 
than  does  the  erigeron,  yet  fortunately  in  no  case  within  the  limita- 
tions of  the  former  ;  the  two  most  nearly  approaching  each  other  be- 
ing No.  1  fireweed  and  No.  3  erigeron,  which  still  show  a  difference 
of  19°  while  the  average  difference,  as  will  be  noticed,  is  69*19°.  It 
will  also  be  seen  that  sample  No.  3  of  erigeron  gives  not  only  the  low- 
est polarizing  angle,  but  is  also  the  lowest  in  sp.  gr.,  and  this  seems  to 
hold  good  in  nearly  all  the  essential  oils  the  spectral  analysis  of 
which  I  have  undertaken.    This  I  found  to  be  caused  by  the  resin 
1  The  importance  of  having  thermometers  in  chemical  analyses,  which 
have  been  standardized  and  corrected  by  the  astronomer  of  Yale  Observatory 
or  some  other  equally  reliable  authority,  cannot  be  over-estimated.  The  wri- 
ter has  found  that  many  finely  constructed  and  expensive  thermometers  which 
he  had  formerly  placed  much  confidence  in,  after  having  been  used  for  some 
time  in  chemical  work,  had  their  readings  changed  fully  10°  O.  (18°  F.),  rend- 
ering them  unfit  for  use.  Thermometers  corrected  and  standardized  can  be 
obtained  at  prices  ranging  from  $5  to  $10. 
