448 
ON  SOME  CONSTITUENTS  OF  RHUBARB. 
IV — Action  of  Nitric  Acid  on  Aporetin, 
When  crude  aporetin  (that  which  we  used  for  these  experi- 
ments contained  phseoretin)  is  brought  in  contact  with  concen- 
trated nitric  acid,  a  red-brown  solution  is  formed,  which  generates 
heat,  and,  evolving  nitrous  fumes,  undergoes  further  decomposi- 
tion ;  if,  after  the  evolution  of  nitrous  fumes  has  somewhat 
ceased,  the  action  be  assisted  by  heat,  taking  care  that  an  excess 
of  nitric  acid  is  present,  it  will  be  observed,  after  boiling  the 
mixture  for  several  hours,  that  a  yellow  substance  deposits,  and 
that  a  further  quantity  may  be  obtained  on  the  addition 'of  water 
to  the  solution  after  it  has  become  cold.  This  yellow  body  is  a 
nitro-compound  of  acid  properties,  and  is  the  principal  product 
of  the  action  of  nitric  acid  on  aporetin. 
The  mother-liquor  is  of  a  dark  yellow  color,  and  gives,  on 
evaporation  (which  is  facilitated  by  adding,  from  time  to  time, 
small  quantities  of  alcohol,  in  order  to  carry  off  the  nitric  acid,  ) 
a  considerable  quantity  of  oxalic  acid,  colored  yellow  with  extra- 
neous matter. 
The  liquor  from  which  the  oxalic  acid  has  been  separated,  gives 
with  alkalies  brownish-red  tints,  in  consequence  of  the  formation 
of  salts  with  an  acid  still  to  be  examined. 
No  picric  or  styphnic  acid  could  be  detected  among  the  pro- 
ducts of  the  action  of  nitric  acid  on  aporetin. 
If  the  yellow  nitro-compound  is  washed  on  a  filter  with  water, 
the  latter  acquires,  after  some  time,  an  amaranth-red  color  ;  if 
the  washing  be  continued  with  considerable  quantities  of  water, 
it  still  continues  to  acquire  a  deep  red  color,  without  diminishing 
materially  the  bulk  of  the  nitro-compound. 
Boiling  water  and  boiling  alcohol  dissolve  the  nitro-compound, 
and  acquire  a  red  color,  but  the  nitro-compound  separates,  on 
the  cooling  of  these  solutions,  as  a  yellow  powder.  Alkaline 
solutions,  when  dilute,  produce,  with  the  nitro-compound,  red 
solutions,  but,  when  concentrated,  a  flocculent  brown  compound 
deposits,  and  the  solutions  become  also  brown,  in  consequence  of 
their  decomposition. 
Concentrated  ammonia,  at  ordinary  temperatures,  forms  a 
beautiful  violet  compound,  part  of  which  precipitates  ;  when  dry, 
it  has  a  bronze  lustre.  The  ammonia  compound  is  soluble  in 
water  with  a  violet  color ;  acids  do  not  precipitate  the  original 
