Am.  Joto.  Pharm.  ) 
Feb.  1,1871.  J 
Lecture  Experiments. 
59 
LECTURE  EXPERIMENTS. 
By  Prof.  A.  W.  Hofmann. 
Translated  by  Prof.  Leeds  from  the  Proceedings  of  the  German  Chemical  Society, 
Berlin,  Vol.  Ill,  No.  12. 
1.  Inflammation  of  hydrogen  combinations  in  contact  with  fuming 
nitric  acid. 
It  is  known  through  the  investigations  of  Graham,  that  phosphuret- 
ted  hydrogen,  which  has  lost  its  spontaneous  inflammability  by  con- 
tact with  sulphur  or  in  any  other  manner,  acquires  it  again  when 
brought  into  contact  with  nitrous  acid.  Phosphuretted  hydrogen  bub- 
bles inflame,  if  a  glass-rod  moistened  vnth  hot  fuming  nitric  acid  be 
held  over  the  surface  of  water  out  of  which  they  are  rising.  When 
some  drops  of  warm  fuming  nitric  acid  are  poured  into  a  cylinder  of 
phosphuretted  hydrogen  gas,  which  does  not  ignite  spontaneously,  an 
extremely  powerful  and  not  altogether  safe  detonation  takes  place. 
Sulphuretted  and  seleniuretted  hydrogen  are  decomposed  in  the 
same  manner  by  fuming  nitric  acid  with  the  phenomena  of  ignition. 
But  if  the  sulphuretted  hydrogen  contains  a  considerable  quantity  of 
free  hydrogen,  the  combustion  does  not  take  place.  It  is  well  then 
in  this  experiment  to  prepare  the  sulphuretted  hydrogen  from  native 
sulphide  of  antimony  and  not  from  sulphide  of  iron. 
This  phenomenon  is  most  strikingly  exhibited  by  hydriodic  acid 
gas.  When  some  cubic  centimetres  of  moderately  warm  fuming 
nitric  acid  are  poured  into  a  rather  large  cylinder  of  hydriodic  acid 
gas,  immediately  a  great  red  flame  bursts  forth,  which  is  enveloped 
in  a  violet  cloud  of  iodine  vapors.  At  the  same  time  the  inside  of 
the  cylinder  is  coated  with  a  network  of  steel-gray  crystals  of  iodine. 
2.  Observation  of  complementary  colors  in  loohing  upon  a  body  with 
transmitted  and  with  reflected  light. 
Many  colored  substances,  as  is  well  known,  show  in  reflected  light 
the  color  which  is  complementary  to  that  which  they  exhibit  in  trans- 
mitted light.  This  phenomenon  is  particularly  beautiful  in  the  case 
of  the  aniline  colors,  especially  in  the  aniline  green  which  is  usually 
termed  iodine  green.  Every  one  is  familiar  with  the  deep  purplish 
red  which  the  salts  of  rose  aniline,  when  in  solution,  show  by  transmit- 
ted light.  He  less  frequently  has  the  opportunity  of  observing  the 
magnificent  cantharides  green  which  the  faces  of  large  crystals  re- 
flect. 
