AmMay?imrm'}        Adulteration  of  Volatile  Oils.  217 
our  aesthetic  development.  Unfortunately,  a  certain  sample  may  be 
pleasing  to  one  and  obnoxious  to  another,  and  this  introduces  a 
serious  problem  in  the  valuation,  namely  the  personal  equation. 
A  vast  amount  of  accurate  work  has  been  done  with  volatile  oils 
in  determining  certain  physical  and  chemical  properties  and  setting 
limits  for  natural  variation,  but  often  the  desirable  or  most  valuable 
portion  which  produces  the  delicate  aroma  is  not  considered.  The 
odorous  constituents  are  often  so  delicate  that  chemical  estimation 
is  impossible.  Their  source  is  not  definitely  known,  but  it  is  thought 
that  they  are  decomposition  products  from  glycosides  brought  about 
by  the  catalytic  action  of  certain  enzymes. 
The  best  practical  method  of  valuation  is  the  comparison  of  odors 
by  experts.  The  nobility  have  their  perfumers,  whose  duty  it  is  to 
blend  and  select  the  odors  to  be  used  at  various  functions.  So 
delicate  has  their  sense  of  smell  become,  that  only  a  few  samples 
are  compared  each  day.  This,  then,  is  the  perfumer's  art,  he 
has  both  the  natural  and  artificial  products  at  his  disposal,  and 
his  duty  it  is  to  combine  them  into  a  perfect  harmony  of  pleasing 
odors.    At  present  it  is  an  art — it  may  become  a  science. 
It  remains  to  be  seen  whether  or  not  there  is  a  relation  between 
the  various  odors  as  there  is  between  musical  tones,  or  of  colors. 
Probably  there  is,  for  some  will  harmonize,  some  detract,  some  in- 
crease, while  others  will  make  a  decided  discord. 
Our  scientific  knowledge  of  odors  is  very  meagre  when  compared 
to  our  knowledge  of  light  and  sound.  Is  the  sense  of  smell  due  to 
small  particles  ?  If  so,  what  is  their  size,  shape  and  rate  of  motion? 
Extreme  smallness  is  not  a  great  barrier  at  the  present  time,  for 
particles  one  thousand  times  as  small  as  the  size  we  have  attributed 
to  molecules  have  been  demonstrated  in  radium  emanations,  and 
these  quite  accurately  studied.  Or,  is  odor  due  to  some  vibration 
in  the  ether,  as  is  light  and  sound?  Until  the  day  dawns  when 
these  things  shall  be  accurately  known,  comparatively  little  progress 
can  be  made  in  the  exact  valuation  of  odors  from  volatile  oils.  Pro- 
fessor Michelson,  the  great  American  physicist,  has  devised  an  instru- 
ment called  the  interferometer,  which  will  measure  the  length  of 
light  waves  so  accurately  that  the  error  is  infinitesimal.  Who  will 
devise  a  way  to  measure  the  odors  of  volatile  oils  and  thus  give  us  an 
exact  scientific  method  of  valuation  for  these  products  ? 
At  present,  undoubtedly,  adulteration  is  being  practised  and  we 
