IODO-SULPHATES  OF  THE  CINCHONA  ALKALOIDS.  247 
Sulphuretted  hydrogen,  soluble  sulphides,  sulphurous  acid  and 
sulphites,  together  with  chlorine  water,  instantly  decolor  their 
alcoholic  solution,  with  the  production  of  hydriodic  acid. 
In  dilute  alcoholic  solutions,  starch  gives  immediate  evidence 
of  iodine,  and  nitrate  of  silver  gives  a  yellowish-white  precipitate 
of  iodide  of  silver,  and  some  organic  basic  compound  which  can 
only  be  removed  by  the  action  of  concentrated  boiling  nitric 
acid ;  this  reaction,  although  commencing  at  the  ordinary  tem- 
perature, with  violent  disengagement  of  nitrous  acid  vapors, 
must  be  perfected  by  boiling. 
Baryta  salts  exhibit  the  existence  of  sulphuric  acid,  which  in 
all  instances  is  an  essential  constituent  in  their  formation. 
The  quinidin  and  cinchonin  salts  dissolve  with  more  difficulty, 
in  consequence  of  their  greater  thickness  and  less  extent  of 
surface. 
Since  the  author  had  the  honor  of  communicating  his  discovery 
of  the  optical  salt  of  cinchonidin  to  the  Royal  Society,  he  has 
ascertained  that  its  primary  form  is,  like  that  of  the  quinine 
salt,  that  of  a  right  rhombic  prism,  and  usually  very  thin. 
Both  the  quinine  and  cinchoni-  f  which  obstruct  plane-polarized 
din  salts  are  derivable  from  the  !  light,  when  their  longer  diameters 
primary  rhombic  prisms,  and  crys-  j  are  parallel  to  the  plane  of  the  po- 
tallize  as  rhomboids  and  /^-prisms    larized  ray. 
f  which  obstruct  the  same  beam  when 
and      .  ms  '  their  longer  diameters  are  perpen- 
r  ]  dicular  to  the  plane  or  the  polarized 
Lray. 
In  Quinine  salt  Jtl-i^b  otoj.- 
t   +i     •    i     .j.      u  (the  rhomb  obtuse  =  137y 
In  the  cmchonidm  salt  $ '         lt  .  ,00 
£  "      "      acute  =  4d° 
A  remarkable  difference  exists  between  the  quinine  and  cin- 
chonidin salt,  which  is,  that  the  optical  crystals  of  the  last  salt, 
if  allowed  to  remain  in  the  mother-solution  with  an  excess  of 
less  than  1  per  cent,  of  sulphuric  acid,  undergo  a  transforma- 
tion, and  become  long,  golden,  silky  aciculoe,  radiating  in  beau- 
tiful globose  tufts  :  this  salt  has  some  doubly  absorbent  powers 
also,  but  very  feeble.  When  this  salt  is  attempted  to  be  redis- 
solved  in  boiling  spirit,  in  order  to  be  recrystallized,  it  does  not 
re-form,  but  the  optical  crystals  are  then  produced  ;  when  the 
silky  crystals  are  carefully  air-dried,  they  retain  their  yellow 
