78 
ON  THE  ODORS  OF  PERFUMES. 
1 
1.  If  an  odorous  substance  can  be  neutralized  or  destroyed 
by  another  odorant  body  there  are  others  destitute  of  odor 
which  by  union  produce  odorant  substances. 
(To  this  class  of  odorless  bodies  belong  0,  S,  Se,  Te,  C,  H, 
As,  Az,  and  we  might  add  P,  which  is  odorless  unless  com- 
bined.) 
2.  Likewise  there  are  odorless  bodies  which  have  become 
odorant  by  union  with  others  endowed  with  odor. 
It  is  thus  with  oxalic,  malic,  butyric,  racemic,  citric,  sorbic 
(the  acid  recently  discovered  by  Hoffmann),  boric,  silicic  acids, 
all  odorless,  which  however  produce  with  the  elements  of  alcohol 
ethers  more  or  less  aromatic. 
3.  It  is  necessary  to  distinguish  those  bodies  which  act  me- 
chanically on  the  olfactory  membranes  (e.  g.?  C1H,  F1H,  BrH, 
IH,  and  the  vapors  of  N03+HO,  S03HO)  from  those  which 
exert  a  physiological  influence  (for  example,  CI,  Br,  I,  N04, 
S02,  the  hydrocarbons,  the  essential  oils,  &c.) 
4.  It  is  necessary  also  to  distinguish  bodies  having  an  odor 
proper,  that  is,  an  odor  which  exists  when  they  form  compounds 
with  other  bodies  (for  example,  arsenic).  The  arsenical  odor  is 
recognized  in  AsH3,  AsBr3,  and  in  the  cacodyl  series.  Tin  is 
another  example.  The  odor  of  tin  characterizes  a  large  num- 
ber of  stannic  compounds.  Sulphur:  thus  S02SH,  S2C,  SNH3, 
SCI,  &c,  are  distinguished  by  a  more  or  less  sulphurous  odor. 
We  might  also  mention  napthaline,  benzoin,  and  other  hydro- 
carbons and  organic  radicals. 
We  see  that  this  group  of  bodies,  characterized  by  a  peculiar 
odor,  embraces  those  elements  which,  like  sulphur,  arsenic  and 
phosphorus,  are  destitute  of  odor,  that  is,  their  odor  is  manifest 
only  in  combination.  If  we  examine  those  phenomena  we  ob- 
serve (a)  that  elementary  bodies  are  usually  destitute  of  odor ; 
(b)  that  in  general  the  least  odorant  compounds  are  oxygen 
compounds  ;  (c)  highly  odorant  compounds  are  usually  those 
containing  hydrogen.  These  seemingly  singular  facts  may  to  a 
certain  extent  be  explained  when  we  remember  that  in  general 
chemical  compounds  become  less  volatile  as  they  fix  oxygen, 
while  by  union  with  hydrogen  they  become  more  volatile.  But 
these  considerations  do  not  explain  all ;  they  do  not  tell  us  why 
CO  and  C02  are  odorless  gases,  while  C12H,  C26H8,  C12H6,  &c, 
&c,  are  odorant. 
