ON  SOME  CONSTITUENTS  OF  RHUBARB. 
449 
yellow  nitro-compound  from  this  solution  (as  is  the  case  when  a 
very  dilute  solution  of  ammonia  is  taken,)  but  a  violet  compound, 
which  is  soluble  in  an  excess  of  acid  with  a  red  color. 
With  a  cold  concentrated  solution  of  carbonate  of  potash,  the 
nitro-compound  forms  a  reddish-brown  crystalline  powder,  which 
dries  with  a  metallic  lustre  ,  it  is  not  very  soluble  in  cold  water, 
but  dissolves  much  more  readily  in  hot  water  with  a  purple  color. 
A  hot  solution  of  carbonate  of  potash  acts  like  a  solution  of 
caustic  alkali,  producing  instantaneously,  with  decomposition,  a 
flocculent  brown  body. 
The  solution  of  the  nitro-compound  in  ammonia  changes  its 
color  upon  the  addition  of  sulphuret  of  ammonium  to  purple,  and 
then  soon  to  a  dark  indigo  blue.  If  an  acid  be  now  added  to 
this  blue  solution,  a  dark  purple  precipitate  is  the  result ;  the 
precipitate  settles  readily,  and  when  washed  with  cold  water  and 
dried,  resembles  indigo.  Water  dissolves  this  blue  body  very 
sparingly,  with  a  purple  color  ;  the  alkalies  dissolve  it,  giving  a 
splendid  blue  solution.  The  blue  compound  is  also  formed  when 
the  solution  of  the  nitro-compound  in  alcohol,  to  which  has  been 
added  a  small  quantity  of  hydrochloric  acid,  is  brought  in  con- 
tact with  metallic  zinc. 
The  dry  nitro-compound,  if  slowly  heated  on  platinum  foil, 
gives  off  yellow  fumes,  leaving  a  carbonaceous  residue ;  if  quickly 
heated,  it  deflagrates,  but  the  combustion  in  this  case  is  also 
incomplete. 
The  behaviour  of  the  nitro-compound  produced  by  the  action 
of  nitric  acid  on  aporetin,  tends  to  prove  that  it  is  identical  with 
chrysammic  acid,  which  is  so  well  characterized  by  its  potash 
salt,  by  its  transformation  into  chrysamminamid,  and  especially 
by  the  formation  of  that  beautiful  blue  compound,  hydro-chrys- 
ammid. 
The  formation  of  chrysammic  acid  from  aporetin  is  of  some 
interest,  inasmuch  as  it  has  hitherto  only  been  obtained  from 
aloes ;  it  is  therefore  our  intention  to  completely  establish  the 
identity  of  this  acid,  as  prepared  from  aporetin,  with  that  result- 
ing from  the  action  of  nitric  acid  on  aloes,  by  analyzing  our 
substances  as  soon  as  we  have  a  sufficient  amount  of  material  at 
command — Quarterly  Journal  of  the  Chemical  Society,  from 
London  JPharm.  Jour.,  May  1,  1858. 
29 
