^"^""DecyiSr""'}        Action  and  Reactions  of  CUnolin.  623 
Picric  acid  (1  part  in  100  parts  water)  gives  a  yellow  amorphous 
precipitate,  soluble  in  alcohol,  more  difficultly  in  hydrochloric  acid, 
and  easily  with  a  reddish-yellow  color  in  solution  of  caustic  potash. 
Limit  of  reaction  :  1  in  17,000. 
Mercuric  chloride  (5  parts  in  100  parts  water)  gives  a  white  iloccu- 
ient  precipitate  that  rapidly  settles,  easily  soluble  in  hydrochloric  acid, 
more  difficultly  in  acetic  acid.  From  dilute  solutions  small  crystalline 
needles  are  formed.    Limit  of  reaction  :  1  in  5,000. 
Iodide  of  potassium  and  mercury  (5  parts  of  potassium  iodide  and 
^  part  of  mercuric  chloride  in  100  parts  of  water)  gives  a  yellowish- 
white  amorphous  precipitate,  which  upon  the  addition  of  hydrochloric 
acid  is  converted  into  delicate  amber-yellow  crystalline  needles  (char- 
acteristic reaction).    Limit  of  the  reaction  :  1  in  3,500. 
Concerning  the  definition  of  the  limits  of  the  last  five  reactions,  the 
most  delicate  for  cliinolin,  it  should  be  remarked  generally,  that  not 
only  the  quantity  of  the  body  upon  which  it  is  to  react,  but  also  that 
of  the  reagent,  should  be  known.  In  every  case  5  cc.  of  the  par- 
ticular reagent  was  added  to  45  cc.  of  water  and  the  dilute  solution 
of  chinolin  salt,  containing  a  known  quantity,  allowed  to  run  in  drop 
by  drop ;  with  the  exception  of  phospliomolybdic  acid,  where  5  cc. 
each  of  phospliomolybdic  and  pure  concentrated  nitric  acid  were  added 
to  40  cc.  of  water. 
The  important  influence  the  proportion  of  the  liquid  to  be  tested  to 
the  reagent  has  upon  the  limit  of  the  reaction  is  shown  by  the  follow- 
ing example:  In  a  mixture  of  60  cc.  of  water  and  15  cc.  of  1  per 
cent,  picric  acid,  1  milligram  of  chinolin  hydrochlorate  produces  a 
permanent  precipitate,  which  would  give  the  limit  of  the  reaction  as  1 
in  75,000 ;  whilst  in  a  mixture  of  70  cc.  of  water  and  5  cc.  of  the 
same  picric  acid, — conseqnentiy  in  the  same  quantity  of  liquid, — a  dis- 
tinct precipitate  first  results  with  7  milligrams  of  chinolin  hydrochlo- 
rate, which  would  give  the  limit  at  about  1  in  11,000. 
Potassium  ferrocyanide  colors  solution  of  a  chinolin  salt  reddish. 
Upon  the  addition  of  a  mineral  acid,  but  not  acetic  acid,  a  reddish- 
yellow  amorphous  precipitate  is  thrown  down,  which  afterwards 
becomes  crystalline.    Limit  of  the  reaction  about  1  in  1,000. 
Solution  of  potassium  ferrocyanide  in  hydrochloric  acid  produces 
in  concentrated  solution  of  chinolin  beautiful  small  crystals. 
Potassium  bichromate,  carefully  added,  forms  delicate  dendritic 
crystals,  soluble  in  excess  of  the  reagent. 
