1 1 8  Hydrobromic  Acid. 
pared  with  water  at  i5'6°C.=6o°F.  It  is  free  from  sulphuric  acid,  or 
gives  but  an  unimportant  trace  when  tested  with  solution  of  baric  chlo- 
ride ;  and  is  free  from  sulphurous  acid  when  tested  by  its  action  on 
pure  zinc  yielding  a  gas  which  does  not  blacken  paper  moistened  with 
solution  of  plumbic  acetate.  It  leaves  on  evaporation  no  residue,  or 
but  an  accidental  trace. 
It  consists  of  about  33'4  per  cent,  of  bromine,  about  0'6  per  cent, 
of  hydrogen,  and  66  per  cent,  of  water  ;  or,  of  34  per  cent,  of  hydro- 
bromic acid,  HBr=8i  and  66  per  cent,  of  water.  Its  formula  is 
(H=i+Br=8o=)  HBr=8i+Aq. 
In  making  this  acid  on  a  scale  suited  to  the  physician  or  pharmacist 
each  part  in  the  formula  may  be  represented  by  28*35  grams=i  ounce 
avoirdupois,  and  the  process  answers  very  well  upon  this  scale,  yield- 
ing about  360  grams— 12*47  ounces. 
Tared  beakers,  a  retort  about  double  the  capacity  of  the  liquid,  with 
a  strip  of  wire  cloth  around  it  where  the  heating  flame  is  applied,  and 
a  small  Liebig's  condenser,  are  necessary  for  this  process,  and  in  the 
distillation  here,  as  indeed  everywhere,  the  lamp  flames  should  be 
applied  to  the  side  of  the  retort. 
If  the  mixture  of  sulphuric  acid  and  water  be  not  cooled  it  causes 
spattering  and  loss  when  poured  into  the  hot  solution  of  the  bromide.  In 
dissolving  the  bromide  in  an  equal  weight  of  water  by  heating,  there 
is  loss  of  water  by  evaporation,  and  unless  this  loss  be  made  up  it  will 
not  be  practicable  to  get  a  perfect  solution.  But  an  entirely  perfect 
solution  is  not  essential,  provided  the  undissolved  portion  be  in  a  finely 
divided  state,  for  when  the  diluted  sulphuric  acid  is  poured  slowly  in 
with  stirring  any  small  proportion  of  the  bromide  will  be  dissolved  by 
the  additional  amount  of  liquid,  and  by  the  stirring.  After  standing 
24  hours  the  lower  part  of  the  vessel  will  be  occupied  by  a  mass  of 
crystals  of  large  size,  easily  broken  up  to  drain  and  wash.  The  quan- 
tity of  sulphuric  acid  taken  for  the  process  appears  disproportionate, 
being  in  excess  of  the  quantity  necessary  to  form  acid  potassium  sul- 
phate ;  but  unless  such  excess  be  taken  the  salt  will  not  crystallize  out 
as  completely,  and  then  the  distillation  will  be  defeated  when  only 
about  half  finished  by  bumping  in  the  retort.  Smaller  proportions  of 
acid  were  successively  tried,  and  when  bumping  occurred  the  process 
was  stopped,  and  the  contents  of  the  retort  were  turned  out,  cooled 
and  the  crystals  separated,  drained  and  washed,  but  this  is  troublesome 
f  Am.  Jour.  Pharm, 
\      Mar.,  1878. 
