94 
Action  of  Nitric  Acid  on  Metals. 
Am.  Jour.  Pliarm. 
Feb.,  1893. 
perfume  in  these  different  regions,  I  have  been  able  to  assure  my- 
self that  the  odor  from  the  upper  surface  of  the  petals  alone  corres- 
ponds to  the  finest  neroli.  The  odor  of  the  flower  then  is  a  mixture. 
The  conclusions  to  be  drawn  from  these  researches  are  : 
(1)  That  the  essential  oil  is  generally  found  localized  in  the 
epidermal  cells  of  the  upper  surface  of  the  petals  or  sepals,  though 
it  may  exist  upon  both  surfaces,  especially  if  the  floral  organs  are 
completely  hidden  in  the  bud.  The  lower  surface  generally  con- 
tains tannin  or  pigments  derived  from  it. 
(2)  The  chlorophyll  seems,  in  every  case,  to  give  rise  to  the 
essential  oil.  This  transformation  is  readily  comprehended  if  it  be 
admitted,  as  is  generally  understood,  that  the  floral  organs  are  but 
modified  leaves  found  performing  a  new  function.  The  chlorophyll 
being  thus  diverted  from  its  original  purpose,  may  be  transformed 
into  tannoid  compounds  or  into  essential  oils. 
(3)  The  liberation  of  perfume  in  the  flower  only  becomes  percep- 
tible when  the  essential  oil  is  sufficiently  freed  from  the  inter- 
mediate compounds  which  have  given  rise  to  it.  Its  formation  is 
to  some  extent  in  inverse  proportion  to  that  of  the  tannin  and  pig- 
ments in  the  flower.  This  will  explain  why  flowers  with  green 
petals  possess  no  odor,  why  white  flowers  or  roses  are  most  fre- 
quently odoriferous,  why  the  Composite  which  are  so  rich  in  tannin1 
have  a  characteristic  disagreeable  odor,  and  why  the  cultivated 
white  lilac  and  forced  roses  acquire  a  very  fine  perfume. 
THE  ACTION  OF  NITRIC  ACID  ON  METALS.2 
By  C.  Montemartini. 
Much  contradiction  exists  as  to  the  changes  which  occur  when 
nitric  acid  acts  on  tin.  The  author  findsjthat  the  acid,  up  to  a 
concentration  of  12  per  cent.,  always  attacks  tin  with  formation  of 
stannous  salt,  which  partially  decomposes,  forming  a  turbid  solu- 
tion; gas  is  always  evolved,  although  slowly.  Nitric  acid  from  12 
to  45  per  cent,  completely  dissolves  the  metal  to  a  yellow  solution, 
with  an  abundant  evolution  of  gas;  the  solution,  when  left, 
slowly  becomes  turbid,  but  the  precipitation  may  be  retarded  by 
1  Daniel,  "  lye  Tannin  des  Composees  "  {Rev.  Gen.  de  Bot.,  ii.  391). 
2  Gazzetta,  22,  384,  397  and  426  ;  Jour.  Chem.  Soc.,  1892,  p.  1402  ;  compare 
also  Amer.  Jour.  Pilar.,  Dec,  1892,  p.  618. 
