lT4         NEW  TEST  FOR  HYDROCYANIC  ACID  IN  VAPOR. 
much  used ;  and  when  iron  is  employed  to  produce  a  black  tint, 
it  requires  for  its  mordants  either  the  pyrogallic  acid  or  the 
hydrosulphate  of  ammonia.  Brown  is  produced  by  the  chloride 
of  gold  alone,  as  also  by  a  solution  of  sulphate  of  copper  with  a 
mordant  of  the  prussiate  of  potash  (ferrocyanide  of  potassium); 
and  titanium,  uranium  and  molybdenum,  judged  by  their  chemi- 
cal behavior,  would  give  rise  to  similar  results.  The  "  golden- 
yellow  color,"  so  much  in  fashion  of  late,  is  produced  by  a  solu- 
tion of  arsenic  with  a  mordant  of  the  hydrosulphate  of  ammonia. 
And  cadmium  would  probably  give  rise  to  a  similar  result.  In 
the  case  of  dyeing  the  lighter  tints,  however,  it  becomes  neces- 
sary to  submit  the  hair  to  a  process  of  bleaching,  which  is 
commonly  effected  by  a  solution  of  one  or  other  of  the  alkalies, 
by  chlorine,  by  the  chloride  of  soda  or  lime,  or  by  sulphurous 
acid,  bisulphate  of  magnesia  or  lime,  or  peroxide  of  hydrogen. 
In  general,  the  dyes  requiring  mordants  do  not  stain  the  epi- 
dermis.— Lond.  Pharm.  Journ.^  Jan.^  1869, /rom  The  British 
Medical  Journal. 
A  NEW  TEST  FOR  HYDROCYANIC  ACID  IN  YAPOR. 
By  M.  Schonbein. 
M.  Schonbein  has  given  to  the  French  Academy  of  Medicine 
a  description  of  a  new  and  extremely  delicate  reagent  for  the 
detection  of  hydrocyanic  acid  in  the  state  of  vapor.  It  consists 
of  paper  imbued  with  resin  of  guaiacum,  and  moistened  with  a 
solution  of  sulphate  of  copper  at  the  moment  of  use.  In  con- 
tact with  hydrocyanic  acid,  the  prepared  paper  immediately 
assumes  a  blue  color.  Three  parts  of  resin  of  guaiacum  are  dis- 
solved  in  a  hundred  parts  of  rectified  spirit.  White  filtering- 
paper  is  steeped  in  this  solution  and  dried.  The  paper  should 
remain  white.  A  solution  is  prepared  of  one  part  of  sulphate 
of  copper  in  five  hundred  parts  of  water.  To  employ  the  test, 
a  slip  of  the  paper  is  moistened  with  this  solution  of  sulphate  of 
copper,  and  brought  in  contact  with  hydrocyanic  acid,  either 
dissolved  in  water  or  diffused  in  the  air,  when  it  immediately  be- 
comes blue.  The  sensitiveness  of  the  reaction  is  shown  by  the 
following  experiments  : — 
