Am  Jour  Pharm.|        Betectiou  of  Nlti'oas  cmcl  Nitric  Acids.  399 
Aug.,  1885.       1  «/ 
DETECTION  OF  NITROUS  AND  NITRIC  ACIDS. 
By  E,.  Warington. 
In  the  present  communication  the  author  gives  the  results  of  experi- 
ments on  the  various  tests  for  nitrous  and  nitric  acid.  The  delicacy 
of  a  test  depends  greatly  on  the  manner  in  which  it  is  applied,  there- 
fore old  as  well  as  new  tests  are  included  in  the  present  note.  In 
nearly  all  cases  blank  experiments  were  made  under  exactly  similar 
conditions  to  those  of  the  test  experiment. 
Detection  of  Nib^ous  Acid.  Iodide  Test. — 1  cc.  of  Trommsdorff's 
reagent  is  added  to  5  cc.  of  nitrite  solution,  and  the  mixture  acidulated 
with  one  drop  of  dilute  sulphuric  acid  (1  in  5);  under  these  conditions 
a  solution  containing  1  part  of  nitrous  nitrogen  per  million  of  water 
soon  caused  an  abundant  liberation  of  iodine,  whilst  1  in  20  millions 
gave  rise  to  a  blue  coloration  in  3  minutes,  and  solutions  containing  1 
in  100,  and  1  in  200  millions,  gave  a  blue  tinge  in  30  and  60  minutes 
respectively.  The  blank  experiment  only  began  to  color  in  4  hours. 
The  metaphenylenediamine  test  is  accelerated  by  warming.  Four  drops 
of  a  solution  containing  5  grams  per  litre,  and  one  drop  of  dilute  sul- 
phuric acid  added  to  5  cc.  of  nitrite  solution,  causes  a  speedy  and  very 
distinct  reaction  with  one  part  of  nitrous  nitrogen  per  million  of  water, 
but  with  1  in  10  millions  the  change  begins  in  2  minutes,  and  the  final 
color  is  only  pale  straw-yellow.  Paramidohenzeiie-azo-diamethylaniline 
test  (Meldona,  Trans.,  1884,  108). — A  solution  containing  O'lO  gram 
of  this  reagent  per  litre  is  employed,  and  one  drop  of  test  solution,  one 
drop  of  dilute  sulphuric  acid,  and  finally  a  slight  excess  of  ammonia, 
are  added  to  5  cc.  of  nitrite  solution.  No  reaction  is  obtained  with 
solutions  containing  1  part  nitrous  nitrogen  per  million  of  water,  when 
the  reagents  are  added  immediately  after  one  another,  but  when  the 
solution  acidified  with  sulphuric  acid  is  heated  for  2  minutes  in  boiling 
watel',  then  on  addition  of  the  ammonia  a  distinct  blue  coloration  is 
obtained  even  with  1  part  of  nitrous  nitrogen  in  10  millions  of  water, 
and  a  pale  sap-green  with  1  in  100  millions.  The  color  is  somewhat 
fugitive.  With  the  iiajphthylamine  test,  using  one  drop  of  saturated  solu- 
tion of  sulphanilic  acid,  one  drop  of  dilute  hydrochloric  acid,  and  one 
drop  of  saturated  solution  of  naphtliylamine  hydrochloride,  as  already 
stated  (Trans.,  1881,  229),  1  part  of  nitrous  nitrogen  in  100  millions 
