AmFeb!;i893ai'm'}      Action  of  Nitric  Acid  on  Metals.  95 
adding  hydrochloric  acid.  The  tin  is  present  in  these  solutions  as 
stannous  nitrate,  and  the  turbidity  is  due  partly  to  the  oxidation  of 
this  salt  and  partly  to  its  conversion  into  insoluble  stannous  com- 
pounds, which,  in  turn,  yield  stannic  hydrate.  Nitric  acid  of  more 
than  45  per  cent,  concentration  does  not  dissolve  tin,  but  converts 
it  into  a  white  substance.  If  70  per  cent,  acid  is  used,  this  white 
oxidation  product  is  soluble  in  water,  but  the  solution,  after  a  few 
seconds  becomes  turbid,  and  stannic  hydrate  is  deposited ;  the 
addition  of  hydrochloric  acid  to  the  clear  solution  greatly  retards 
the  precipitation.  The  soluble,  white  substance  is  found  by  analysis 
to  be  stannic  nitrate,  Sn(NOs)4 ;  it  is  stable  in  presence  of  concen- 
trated nitric  acid  at  900,  but  is  immediately  decomposed  at  ioo°. 
The  solution  of  1  gram  of  tin  in  excess  of  27-5  per  cent,  acid 
yields  0  0180  gram  of  ammonia,  01060  gram  of  nitrous  oxide,  and 
0-0051  gram  of  nitrogen.  The  maximum  quantity  of  ammonia  is 
obtained  when  1  per  cent,  nitric  acid  is  used,  but  the  rate  of  diminu- 
tion in  the  amount  of  this  gas  produced,  as  stronger  acid  is  used,  is 
small;  even  70  per  cent,  acid  causes  the  formation  of  much  ammonia. 
The  hypothesis  that  the  nitric  acid  is  reduced  by  nascent  hydrogen 
is  insufficient  for  the  explanation  of  the  phenomena  observed  during 
the  action  of  nitric  acid  on  tin. 
Contrary  to  the  statements  of  Personne  (Bull.  Soc.  Chim.,  1864,  i, 
163)  and  Maumene  (Ann.  Chim.  Phys.  [4],  3,  343),  the  action  on 
antimony  of  nitric  acid,  varying  in  concentration  from  2  to  70-27 
per  cent.,  does  not  yield  appreciable  quantities  of  ammonia;  2  per 
cent,  acid  has  very  little  action  on  the  metal.  Antimony  is  not 
dissolved  by  nitric  acid;  a  white  powder  always  remains;  when  70 
per  cent,  acid  is  used,  this  residue  seems  to  have  the  composition 
>(SbO)N03.  Nitric  peroxide  is  practically  the  sole  gas  produced 
when  this  metal  is  used. 
Molybdenum  is  attacked  by  3  to  70  per  cent,  acid  without  the 
formation  of  ammonia.  Concentrated  acid  (70  per  cent.)  attacks  the 
metal  but  slowly;  a  much  more  vigorous  action  occurs  with  weaker 
acid  (50  per  cent.)  and  a  reddish  solution  and  residue  are  obtained. 
The  solution  reduces  permanganate,  so  that  the  metal  is  not  imme- 
diately converted  into  molybdic  anhydride  by  50  per  cent,  acid,  but 
a  nitrate  would  seem  to  be  first  formed;  70  per  cent,  acid  at  once 
gives  molybdic  anhydride.  The  quantity  of  nitric  oxide  produced 
in  the  reaction  between  nitric  acid  and  molybdenum  decreases^as 
