1  50  Relation  of  Acids  of  Nitrogen  to  Sulphuric  Acid.  { ^"^k^aXx^so^'"'" 
specific  gravity  of  1*55  the  sulphuric  acid  becomes  yellow,  and  hence- 
it  was  supposed  that  the  greater  part  of  the  nitrogen  tetroxide  was- 
simply  dissolved.  Acid  of  1*49  specific  gravity  takes  a  greenish-yellow 
color;  acid  of  1*41  specific  gravity  takes  an  intense  green  color;, 
acid  of  1*31  specific  gravity  becomes  blue  and  liberates  n-itrogen- 
dioxide,  which  escapes  with  violent  ebullition  on  gently  heating. 
The  green  and  blue  colors  were  supposed  to  be  due  to  the  formation  of 
nitrous  acid,  the  nitrogen  tetroxide  having  been  decomposed  into  that 
substance  and  nitrogen  dioxide.  As  these  results  are  very  important  to- 
vitriol  manufacturers,  the  author  studied  them  more  accurately,  and, 
as  far  as  possible,  quantitatively.  The  nitrogen  tetroxide,  prepared  from 
dry  fused  lead  nitrate,  was  measured  off^  from  a  burette,  and  mixed  with 
pure  sulphuric  acid,  which  had  been  diluted  to  different  strengths  with 
water,  and  the  effects  of  heat  upon  these  mixtures  were  also  noted. 
The  following  are  given  as  examples  of  the  method  employed  and  of 
the  results  obtained  by  the  author  in  carrying  out  the  experiments  : 
100  cc.  sulphuric  acid  of  1.84  specific  gravity,  to  which  was  added 
2  GC.  =  3  grams  liquid  nitrogen  tetroxide,  gave  a  colorless  solution  with 
a  very  feeble  odor,  recalling  that  of  ozone.  The  amount  of  nitrogen 
dioxide  evolved  from  i  cc.  of  this  solution  in  the  nitrometer  was  deter- 
mined, and  also  the  amount  required  to  decolorize  10  cc.  seminormal 
potassium  permanganate  solution.  From  the  results,  the  author  calcu- 
lates that  his  nitrogen  tetroxide  contained  of  pure  nitrogen  tetroxide  93, 
per  cent.,  and  of  nitric  acid  7  per  cent.;  but  he  argues,  as  in  reality  the 
nitrogen  tetroxide  does  not  exist  as  such  in  the  sulphuric  acid,  but  has 
undergone  a  decomposition,  one  part  of  the  tetroxide  having  been  con- 
verted into  nitric  acid  at  the  expense  of  the  oxygen  of  the  other  part,, 
whilst  the  part  which  has  been  robbed  of  its  oxygen  remains  as  nitrous 
acid  in  combination  with  the  sulphuric  acid  ;  then  assuming  that  this- 
lower  oxide  takes  the  oxygen  from,  and  decolorizes  the  potassium  per- 
manganate, this  would  give  46'5  per  cent,  as  nitrous  acid,  and  53.5  per 
cent,  as  nitric  acid.  The  other  calculations  are  made  on  this  supposi- 
tion, that  is,  it  is  first  assumed  that  all  the  nitrogen  tetroxide  remains  as. 
such,  and  the  deficiency  in  the  theoretical  amount  of  oxygen  required 
is  calculated  as  nitric  acid  ;  but  if,  on  the  contrary,  the  amount  of  oxy- 
gen required  be  less  than  that  found  by  the  permanganate  process,  then- 
he  assumes  that  no  nitric  acid  is  present,  but  that  nitrous  acid  must 
have  been  originally  present  as  an  impurity. 
(I.)  The  acid  was  heated  to  280°,  and  kept  at  that  temperature  for 
