'•}       Action  of  Nitric  Acid  on  Metals.  619 
NH3. 
HN02. 
N20. 
N. 
NO. 
Total 
grams. 
Cadmium,  .... 
0*00197 
0-00695 
0-00570 
0*00033 
0*00216 
0*01691 
0-02493 
0  00195 
0-00422 
0*00045 
0-03553 
Nickel,  
0*01874 
0 '00060 
0*00749 
0*00071 
0*02754 
Cobalt,  
0-02538 
0*00077 
0*00927 
0*00467 
0*04009 
These  numbers  agree  neither  with  the  hypothesis  that  the  dissolu- 
tion of  the  metal  is  accompanied  by  the  formation  of  nascent  hydrogen, 
nor  with  that  of  the  direct  oxidation  of  the  metal  by  the  acid.  No 
hydroxylamine  is  found  amongst  the  final  products  of  the  reaction; 
this  compound,  if  formed,  must  therefore  be  immediately  destroyed 
by  a  secondary  reaction.  The  nitric  oxide  is  always  of  secondary 
origin,  being  derived  in  the  case  of  cadmium,  nickel  and  cobalt 
from  the  decomposition  of  nitrous  acid,  and  in  the  case  of  iron  partly 
from  the  same  source  and  partly  from  the  oxidation  of  the  ferrous 
salts  first  formed.  The  author  holds  that  nitric  acid  acts  as  an 
oxidizing  agent  in  conjunction  with  the  water  present,  the  latter 
entering  into  the  reaction. 
The  investigations  were  also  extended  to  zinc.  The  products 
formed  in  the  reaction  at  a  low  temperature  when  the  acid  is  in 
large  excess  are  nitrous  acid,  hyponitrous  acid,  nitric  oxide,  nitric 
peroxide,  nitrous  oxide,  nitrogen  and  ammonia.  Under  the  con- 
ditions mentioned,  hydroxylamine  is  not  found  among  the  final 
products  of  the  reaction,  and  free  hydrogen  is  never  evolved.  With 
the  exception  of  nitrous  acid  and  nitric  peroxide,  the  above  products 
are  formed,  whatever  the  degree  of  concentration  of  the  acid  ;  no 
nitrous  acid  is,  however,  formed  if  the  solution  contains  more  than 
30  per  cent,  of  nitric  acid,  and  no  nitric  peroxide  if  it  contains  less. 
Ammo7iia. — At  a  temperature  of  3-80,  the  quantity  in  solution 
rises  rapidly  until  the  concentration  of  the  acid  is  10  per  cent.,  then 
slowly  until  a  maximum  is  attained  between  40  and  45  per  cent.;  it 
falls  abruptly  at  47  per  cent.,  and  at  53  per  cent,  only  a  very  small 
quantity  is  producted,  which  gradually  diminishes  with  increased 
concentration,  and  may  be  represented  by  a  straight  line  passing 
through  the  zero  point  at  100  per  cent.  At  a  temperature  of  85 °, 
the  maximum  occurs  at  a  concentration  of  9  per  cent.,  when  it  is 
equal  to  the  production  at  the  lower  temperature ;  it  then  falls 
