^"'"S^jm  ""']  Analysis  of  Coal-tar  Coloring  Matters. 
97 
until  oxygen  has  been  added.  Nitrogen  and  nitrous  oxide  are  also 
liberated. 
In  all  the  previous  experiments,  excess  of  nitric  acid  was  employed 
and  the  temperature  was  kept  constant  (15-200). 
The  metals  may  be  classed  in  three  groups,  according  to  their 
behavior  towards  nitric  acid.  To  the  first  group  belong  those 
metals  which,  with  nitric  acid,  yield  only  nitrous  acid,  nitric  oxide, 
nitrogen  trioxide,  and  nitric  peroxide.  Metals  of  the  second  group 
give,  besides  these  products,  hyponitrous  acid,  nitrous  oxide,  nitro- 
gen and  ammonia.  In  addition  to  these,  metals  of  the  third  group 
liberate  hydrogen.  It  is  to  be  noted  that  metals  belonging  to  the 
first  group  either  do  not  decompose  water  at  all  or  only  at  very 
high  temperatures.  Metals  of  the  second  group  decompose  water 
at  much  lower  temperatures,  and  those  of  the  third  group  act  on 
water  either  at  ordinary  or  at  comparatively  low  temperatures. 
There  is  hence  a  relation  between  the  products  of  the  action  of 
nitric  acid  on  metals  and  the  behavior  of  the  metals  towards  water; 
this  relation  supports  the  author's  view  that  water  sometimes  takes 
part  in  the  reaction. 
The  author  considers  that  the  reaction  between  nitric  acid  and 
metals  which  do  not  decompose  water  may  be  represented  by  the 
equation 
M  -I-  3HNO3  =  M(N03)2  -f  HN02  +  H20, 
or  M  -f  4HNO3  =  M(N03)2  4-  2N02  +  2H20, 
according  as  the  acid  used  is  dilute  or  concentrated.    To  explain  the 
formation  of  nitrogen  trioxide,  the  following  equation  is  employed, 
2M  -f  6HNO3  =  2M(NOs)2  +  N2Os  -f  3H20.   When  water  plays  a 
part  in  the  reaction,  a  more  complex  series  of  equations  is  necessary. 
QUALITATIVE   ANALYSIS   OF   COAL-TAR  COLORING 
MATTERS.1 
By  A.  G.  Green. 
It  is  of  importance  to  dealers  in,  as  well  as  manufacturers  of, 
these  dyes  that  they  should  have  the  means  to  match  colors,  not 
only  in  respect  to  shade,  but  also  in  accordance  with  the  chemical 
constitution  of  any  unknown  colors  which  may  be  submitted  to 
1  Read  before  the  Society  of  Chemical  Industry  ;  Abstract  republished  from 
Chemist  aud  Druggist,  January  14,  1893,  p.  43. 
