rochleder's  proximate  analysis. 
369 
(Continued  from  page  184.) 
sumes  a  violet  color.  Keference  must  be  made  to  these  circumstances  in 
the  employment  of  perchloride  of  iron.  The  perchloride  of  iron  itself  is 
distinctly  colored  yellow  in  considerably  diluted  aqueous  solutions.  On 
this  account,  it  is  necessary  to  prevent  any  excess  of  this  solution,  as  other- 
wise misconceptions  will  arise ;  for  example,  a  blue  coloration  should  be 
observed,  but  instead  of  it  a  green  makes  its  appearance,  because  the 
blue  coloration  which  the  substance  and  the  perchloride  of  iron  produce  is 
converted  into  green  by  the  yellow  of  the  solution  of  perchloride  of  iron 
which  has  been  added  in  excess.  Further,  it  is  always  convenient  to  add 
a  little  ammonia  to  the  fluid  which  has  assumed  a  distinct  color  with  per- 
chloride  of  iron,  to  observe  the  appearances  which  are  thereby  developed. 
The  green  or  blue  coloration  is  changed  by  perchloride  of  iron  sometimes 
into  a  dark  violet,  sometimes  into  a  black,  and  sometimes  into  a  red. 
Thus  the  presence  of  two  substances  can  be  rendered  evident,  which  be- 
have in  a  free  state  quite  the  same  as  perchloride  of  iron. 
2.  Perchloride  of  tin. — The  aqueous  solution  of  perchloride  of  tin  pro- 
duces  no  coloration  in  the  watery  solutions  of  many  substances,  and  also 
no  precipitates  ;  on  the  contrary,  in  the  solutions  of  other  bodies,  a  char, 
acteristically  colored  precipitate  frequently  results  thereby,  sometimes 
only  after  the  addition  of  a  little  ammonia.  Frequently,  by  heating  a  so- 
lution after  the  addition  of  perchloride  of  tin,  a  precipitation  results  which 
contains  no  longer  the  original  substance,  but  a  decomposition  product  of 
the  substance  combined  with  oxide  of  tin. 
3.  Protochloride  of  tin. — The  protochloride  of  tin,  as  a  powerful  agent 
of  reduction,  produces,  particularly  at  elevated  temperatures,  changes  of 
eolor,  which  indicate  the  presence  of  a  body  which  otherwise  might  have 
been  overlooked.  By  this  reducing  action  a  colored  fluid  often  results. 
In  many  cases  the  addition  of  a  little  free  alkali  assists  considerably  the 
action  of  the  protochloride  of  tin. 
4.  Nitrate  of  silver. — By  the  watery  solution  of  this  salt  a  precipitate 
of  a  silver  compound,  insoluble  in  water,  often  results  in  solutions,  par- 
ticularly after  the  addition  of  a  little  ammonia.  Many  of  these  silver  salts 
are  almost  immediately  decomposed  under  the  separation  of  metallic  silver, 
others  only  under  the  influence  of  a  higher  temperature.  The  silver  sepa- 
rates thereby  sometimes  as  a  shining  mirror,  sometimes  as  a  pulverulent 
black  mass.  This  varied  behavior  of  the  different  constituents  of  vege- 
table substances  to  the  solution  of  nitrate  of  silver,  by  the  presence  and 
absence  of  an  alkali,  permits  the  employment  of  this  salt  likewise  for  the 
detection  of  individual  constituents  in  a  mixture. 
5.  Acetate  of  lead. — The  neutral  acetate  of  lead  is  employed  as  a  watery 
as  well  as  a  spirituous  solution ;  for  the  latter  spirit  of  specific  gravity 
•825  is  used.  The  majority  of  organic  substances  are  precipitated  by 
sugar  of  lead  from  a  watery  or  spirituous  solution.  One  part  of  the  lead 
compound,  insoluble  in  spirit  or  water,  dissolves  in  acetic  acid  :  another 
24 
