184 
rochleder's  proximate  analysis. 
have  there  described  a  number  of  reagents  which  are  serviceable  in  the 
majority  of  cases,  whose  behaviour  is  known  to  organic  bodies,  and  which 
every  body  is  in  a  position  to  prepare  or  to  procure  more  readily  than 
others.  I  have  only  appended  those  remarks  to  each  test  which  did  not  ap- 
pear superfluous  in  reference  to  the  objects  of  the  present  instructions  for 
the  analysis  of  vegetable  substances. 
1.  Perchloride  of  iron,  prepared  by  dissolving  dry  crystallized  perchloride 
of  iron  in  water.  A  great  number  of  organic  bodies  afford  with  a  solu- 
tion of  perchloride  of  iron,  when  it  is  added  to  their  aqueous  solutions, 
neither  a  precipitate  nor  a  coloration.  Many  of  the  most  widely-spread 
constituents  of  plants  behave  in  their  aqueous  solution  exactly  as  though 
this  reagent  was  added  to  pure  water.  On  the  contrary,  not  a  few  com- 
pounds exist  which  give  this  reagent  a  remarkable  coloration,  or  are  entirely 
precipitated,  whereby  the  color  of  the  precipitate  is  generally  a  conspicuous 
one.  There  cannot  be  any  conclusion  drawn  on  the  nature  of  a  body 
which  is  contained  in  this  solution,  from  the  coloration  which  a  solution 
of  perchloride  of  iron  assumes,  or  from  the  color  of  the  precipitate  produced 
by  this  reagent.  Morphine,  gallic  acid,  and  the  aldehyde  of  salicylic  acid, 
bodies  which  belong  to  three  different  classes,  behave  very  analogous  to  a 
solution  of  perchloride  of  iron.  Nevertheless,  this  reagent  is  very  service- 
able,  inasmuch  as  bodies  which  produce  with  other  reagents  very  few  cha- 
racteristic reactions,  show  by  this  reagent  when  they  are  mixed  in  very  small 
quantities  with  other  bodies.  A  great  number  of  vegetable  substances 
afford,  when  their  aqueous  solutions  are  mixed  with  a  solution  of  perchlo- 
ride of  iron,  a  dark  green  or  blue  coloration,  as  is  well  known.  Tannin, 
gallic  acid,  and  many  other  similar  bodies,  exhibit  this  behaviour.  Other 
substances  acquire  an  intense  red  color  when  their  solutions  are  mixed  with 
perchloride  of  iron.  It  is  always  advisable  to  add  the  perchloride  of  iron 
in  very  small  quantities  to  the  fluid  under  examination,  as  frequently  the 
color  which  makes  its  appearance  by  a  smaller  quantity  of  this  salt  is  de- 
stroyed by  a  larger  quantity.  There  are  substances  which,  by  the  addition 
of  this  reagent,  acquire  an  intense  color,  but  the  color  soon  disappears 
again,  and  cannot  be  reproduced,  while  with  other  bodies  a  coloration 
results  which  long  remains  unchanged.  The  coloration  effected  by  perchlo- 
ride of  iron  is  often  made  to  disappear  more  quickly  by  the  application  of 
heat.  The  coloration  which  is  developed  by  perchloride  of  iron  in  the  solu- 
tion of  a  substance  is  often  quite  different,  according  as  the  substance  is 
present  in  a  free  condition,  or  combined  to  an  acid,  or  to  a  base.  Frequently 
it  depends  on  the  nature  of  this  acid  or  base  whether  a  coloration  is  de- 
veloped or  not.  It  is  a  known  fact,  that  not  all  morphine  salts  exhibit 
an  equally  intense  blue  coloration  when  mixed  with  perchloride  of  iron, 
which  is  shown  with  some  morphia  salts  every  time  this  reagent  is  added. 
Kinic  acid  in  a  free  state,  in  an  aqueous  solution,  is  colored  intensely  green 
by  perchloride  of  iron,  while  after  its  neutralization  with  ammonia  it  as- 
(To  be  continued.) 
