68  Chemistry  of  Alkaloid  Estimations.     {February a™* 
solution — that  is  potassium  iodide  plus  iodine — was  in  most  cases 
variable  and  depended  upon  conditions  of  concentration,  etc. 
To-day  this  method  of  estimating  alkaloids  by  the  amount  of  iodine 
consumed  in  their  precipitation  is  rarely  mentioned. 
The  fact  that  these  general  alkaloidal  precipitants,  while  valuable 
in  the  detection  and  the  isolation  of  alkaloids,  are  no  longer  used 
for  their  quantitative  determination,  makes  of  especial  interest  the 
recent  publications  in  regard  to  a  new  precipitant  which  is  claimed 
to  form  very  insoluble  compounds  of  definite  composition  with 
nearly  all  alkaloids.  The  reagent  has  been  called  picrolonic  acid 
from  the  fact  that  its  behavior  with  alkaloids  closely  corresponds  to 
that  of  trinitrophenol  or  picric  acid.  It  was  first  investigated  by 
Knorr,  the  discoverer  of  antipyrin.  The  following  structural 
formulas  indicate  its  relationship  to  antipyrin  and  pyramidon: 
C6H4(N02)  b)  (C6H5)  c)  (C6H5) 
/  /  / 
N  N  N 
0=C5    2N  0=C5    2N-(CH3)  0-C5  2N-(CH8) 
QX        |       ||=C10H8O5N4  I        I  -  II 
H^N=C-3C-(CH3)  H-C4--3C-(CH3)  (CH,)2N-C4-=3C-(CH8) 
(a)  Picrolonic  acid  or  i-paranitrophenyl-3-methyl-5  keto-i,  2- 
diazol-4-nitric  acid  ; 
or  i-paranitrophenyl-3-methyl-pyrazolon-nitric  acid. 
(b)  Antipyrin  or  i-phenyl,  2,  3-dimethyl,  5-keto,  I,  2-diazol  or 
i-phenyl,  2,  3-dimethyl-pyrazolon. 
(c)  Pyramidon  or  i-phenyl,  2,  3-dimethyl,  4-dimethylamino-5- 
keto,-i,  2  diazol ; 
or  i-phenyl,  2,  3-dimethyl,  4-dimethylamino-pyrazolon. 
The  substance  may  be  looked  upon  as  a  nitrate  in  which  one 
oxygen  atom  of  nitric  acid  has  been  replaced  by  the  organic  radicle. 
If  this  is  done  its  behavior  with  alkaloids  is  evident. 
Just  as  ammonia  combines  with  nitric  acid  to  form  ammonium 
nitrate,  or,  in  accordance  with  present  theories  of  chemistry,  just 
as  ammonia  combines  with  water  to  form  ammonium  hydroxide 
and  ammonium  hydroxide  reacts  with  hydrogen  nitrate  to  form 
ammonium  nitrate  and  water,  thus  : 
NH3  -f-  HNO3  =  NH3.  HN03; 
or  NHS  +  H20  =  NH4OH 
NH4OH  +  HNO3  =  NH4N03  +  H20. 
