WEEDS  OP  WESTERN  PEPPERMINT  PLANTATIONS.  123 
given,  so  I  am  inclined  to  think  few  crops  are  much  affected  with 
this  weed,  Erigeron  being  the  chief  cause  of  adulteration ;  by 
*  weedy  oil'  is  commonly  meant  that  containing  Erigeron  (that 
is,  in  this  vicinity). 
"  Oils  are  often  colored  by  rust  from  the  boilers  and  pipes, 
and  by  causes  I  am  unable  to  give  as  yet ;  perhaps  too  much 
heat,  or  by  reason  of  the  mint  being  cut  too  green  or  young. 
Formerly,  when  copper  stills  were  used,  the  oil  was  milky  in 
appearance,  and  was  then  all  filtered  (through  paper).  Most  of 
the  oil  is  sent  away  (generally  to  New  York)  after  one  distilla- 
tion, but  occasionally  a  bad  looking  lot  is  re-distilled,  or  filtered 
through  animal  charcoal  and  sand,  the  filtering  said  to  waste  less 
and  take  away  all  color.  I  do  not  hear  of  any  further  process 
of  rectifying  mint  oil." 
The  information  contained  in  this  letter  is  of  great  interest, 
and  if  Mr.  Ensign  carries  out  his  intention  of  sending  me  samples 
of  the  various  oils,  it  is  not  improbable  that  some  chemical  tests 
may  be  observed,  which  may  be  of  value  for  detecting  the  usual 
impurities. 
The  point  which  has  been  undisputably  settled  is  that  Erigeron 
eanadense  is  the  pest  of  the  western  mint  fields,  and  the  admix- 
ture of  the  oil  of  peppermint  with  the  oil  of  this  weed  I  believe 
is  calculated  to  explain  several  circumstances.  Our  American 
oil  of  peppermint  is  exported  to  Europe  in  considerable  quanti- 
ties, but  both  in  Europe  and  this  country  it  does  not  command 
the  price  of  European  oil,  the  latter  being  usually  rectified,  and 
much  superior  in  odor  to  our  more  rank  American  oil.  Careful 
distillation  of  well  selected  fresh  herb,  and  subsequent  careful 
rectification,  may  remedy  this  defect. 
Pure  rectified  oil  of  peppermint,  when  exposed  to  the  air, 
thickens  very  slowly,  while  some  of  our  commercial  oil  in  a  com- 
paratively short  time  acquires  the  consistence  of  sweet  oil,  and 
is  even  turned  into  a  thicker  oleoresinous  liquid.  This  is  proba- 
bly due  to  the  presence  of  oil  of  Erigeron ;  the  latter  at  least, 
when  kept  in  partly  filled  vials,  which  are  occasionally  opened, 
soon  becomes  thick,  and  finally  forms  a  transparent  varnish. 
Commercial  oil  of  erigeron  is  but  little  acted  upon  by  powdered 
