ON  NITRO-PRUSSIDE  OF  SODIUM. 
415 
ence  of  a  little  alcohol,  ether,  or  sugar,  with  a  solution  with  the 
strychnia,  destroys  the  test  immediately,  and  instead  of  the  violet 
color,  a  green  color  is  produced  ;  whereas,  in  similar  circumstances, 
by  the  use  of  his  test,  the  characteristic  violet  color  is  produced, 
being  little  affected  by  the  presence  of  these  substances.  From  a 
series  of  comparative  trials  with  both  these  tests,  Dr.  Davy  finds 
that  the  vegetable  matter  in  ale  and  porter  has  a  less  injurious 
effect  with  his  test  than  with  that  of  M.  Lefort.  In  cases  where 
strychnia  is  present  along  with  organic  matter,  Dr.  Davy  recom- 
mends that  the  latter  should  first  be  separated  as  much  as  possible 
from  the  strychnia,  by  means  of  some  of  the  methods  in  use  for 
that  purpose,  as  the  presence  of  organic  matters  interferes  more  or 
less  with  the  application  of  either  one  or  the  other  test,  and  in 
both  tests  it  is  necessary  that  the  sulphuric  acid  employed  should 
be  undiluted,  for  he  finds  that  if  the  acid  be  much  weaker  in  strength 
than  that  of  a  specific  gravity  1.488,  the  desired  effect  will  not  be 
produced.  M.  Lefort's  test  for  the  detection  of  strychnia  is  pre- 
pared by  moistening  this  alkaloid  with  undiluted  sulphuric  acid, 
and  then  adding  to  it  a  little  bichromate  of  potass,  when  a  fine 
violet  color  is  produced.  This  method  has,  as  is  well  known,  been 
commonly  considered  as  the  most  delicate  and  characteristic  test 
for  the  detection  of  strychnia,  even  when  in  combination  with  or- 
ganic matters  of  various  descriptions. — Annals  of  Pharmacy. 
ON  THE  PREPARATION  OF  NITRO-PRUSSIDE  OF  SODIUM, 
By  A.  Overbeck. 
The  salt  discovered  by  Playfair,  which  is  produced  with  evolution 
of  oxide  of  nitrogen,  cyanogen,  nitrogen  and  carbonic  acid,  by  the 
action  of  nitric  acid  upon  prussiate  of  potash,  is  only  separated 
with  difficulty  from  some  substances  which  are  also  dissolved  in  the 
fluid.  From  this  fluid,  which  is  brown,  nitrate  of  potash  and  oxa- 
mide  separate  ;  and  after  neutralization  with  carbonate  of  soda  and 
subsequent  heating,  a  green  or  brown  precipitate  is  deposited. 
The  separation  of  Playfair's  salt  from  the  nitrate  of  potash  by 
Playfair's  process,  has  given  the  author  no  satisfactory  result,  be- 
cause the  selection  of  the  two  kinds  of  crystals  is  very  wasteful  of 
time.  Kyd  also  appears  to  have  succeeded  no  better,  since  he  has 
adopted  another  course.    The  author  could  not  find  the  point  at 
