Am.  Jour.  Pharm. 
July,  1903. 
Alkaloidal  Color  Tests. 
335 
describe,  and  the  color  frequently  changes  from  one  shade  to 
another  so  gradually  that  mistakes  may  easily  arise.  Even  in  the 
inorganic  world,  where  certain  colors  are  developed  as  the  result  of 
chemical  combinations,  we  seldom  trust  ourselves  with  such  infor- 
mation as  positive ;  for  example,  in  precipitating  a  soluble  com- 
pound of  arsenic  with  a  sulphide,  we  have  produced  an  almost  in- 
fallible indication  that  arsenic  is  present;  but  what  chemist  is  there, 
who  would,  without  further  submitting  this  precipitate  to  the  other 
searching  tests  that  we  possess,  for  absolutely  identifying  the  pres- 
ence of  arsenic,  say  that  arsenic  is  present,  without  a  question  oi 
doubt,  simply  from  the  color  produced  as  the  result  of  the  formation 
of  a  chemical  compound.  Again,  on  passing  hydrogen  sulphide 
gas  into  a  solution  of  mercuric  chloride,  we  have  formed,  as  we  think, 
a  definite  chemical  compound,  and  yet,  who  has  not  seen  the  various 
shades  of  precipitate  that  result  when  the  above  operation  is  per. 
formed  ? 
The  quality  of  the  reagents  seems  to  have  been  lost  sight  of  in  a 
large  measure.  It  is  an  open  secret  that  pure  and  even  C.  P.  molyb- 
dic  acid,  the  chief  constituent  of  Frohde's  reagent,  contains  as  much 
as  15  per  cent,  of  ammonium  nitrate  and  sulphate  or  the  corres- 
ponding salts  of  sodium.  Recently  quotations  were  seen  for  C.  P.. 
phosphomolybdic  acid,  varying  from  $1.45  to  $11.00  per  pound. 
These  examples  incite  thought.  Do  the  reagents  employed  by  the 
various  workers  the  world  over  vary  in  quality  as  the  above  prices  ? 
How  are  the  color  reactions  of  Frohde's  reagent  affected  by  the 
impurities  of  molybdic  acid  ? 
Within  the  last  quarter  of  a  century  there  have  been  isolated  a 
large  number  of  ptomaines,  some  of  which  give  color-reactions 
similar  to  those  of  certain  alkaloids. 
In  connection  with  the  above  we  must  not  forget  to  mention  im- 
perfection of  vision  (color-blindness),  which  plays  such  an  important 
part  in  the  affairs  of  mankind.  In  general,  therefore,  color  reactions 
can  be  considered  useful  only  as  guides  and  should  never  be  con- 
sidered conclusive  in  themselves. 
Strychnine  is  one  of  the  few  alkaloids  that  toxicologists  and  alka- 
loidal chemists  have  pointed  to  with  some  gratification  as  being 
singularly  invulnerable  to  the  attacks  made  on  color  reactions  from 
time  to  time,  it  being  characterized  by  an  infallible  display  of  succes- 
sive color  reactions  ;  and  the  writer  believes  that  the  successive  color 
