Am.  Jour.  Pharm.  1 
Mar.,  1878.  J 
Hydrobromic  Acid. 
117 
the  same  bromine  effect  in  medicine.  But  an  acid  of  this  strength 
would  be  unnecessarily  difficult  to  make  and  to  dispense.  The  next 
most  simple  relation  is  to  have  an  acid  of  half  the  bromine  strength  of 
the  salt,  or  34  per  cent.  Such  a  strength  can  be  made,  kept  and 
dispensed  without  unusual  difficulty,  and  represents  the  bromine  of  the 
potassium  bromide  in  the  proportion  of  about  2  to  1,  a  relation  easily 
remembered,  and  convenient  in  use.  Therefore  this  strength  has  been 
adopted  as  a  proper  and  convenient  one,  and  the  quantity  of  such  an 
acid  equal  to  the  bromine  of  20  grains  of  potassium  bromide  would 
be  40  grains,  though  the  equivalent  dose  might  be  smaller  to  produce 
a  given  effect,  should  bromine  when  combined  with  hydrogen  prove 
more  active  than  when  combined  with  potassium. 
The  formula  and  process  for  making  an  acid  of  this  strength  are  as 
follows  : 
Take  of  Potassium  Bromide,  Six  parts. 
Sulphuric  Acid,  s.  g.  at  i5-6°C.=-6o°F.  1  c 
o  o    .      dr.        qp     o  o  r  Seven  parts. 
1-838,  at  25°C.=77°F.  1828.        j  r 
Water,  Nine  parts. 
Add  to  the  sulphuric  acid  one  part  of  the  water  and  cool  the  mix- 
ture. Then  dissolve  the  potassium  bromide  in  six  parts  of  the  water 
by  means  of  heat,  supplying  the  loss  of  water  by  evaporation  during 
the  heating.  Pour  the  diluted  sulphuric  acid  slowly  into  the  hot  solu- 
tion with  constant  stirring,  and  set  the  mixture  aside  for  24  hours  that 
the  sulphate  of  potassium  may  crystallize.  Pour  off  the  liquid  into  a 
retort,  break  up  the  crystaline  mass,  transfer  it  to  a  funnel,  and  having 
drained  the  crystals,  drop  slowly  upon  them  two  parts  of  the  water  so 
as  to  displace  and  wash  out  the  acid  liquid.  Add  trie  liquid  thus  drained 
off  and  washed  out,  to  that  in  the  retort,  and  distill  the  whole  nearly  to 
dryness,  or  until  nothing  further  distills  off  by  moderate  heating.  The 
distillate  will  weigh  about  ten  parts  and  should  contain  about  37  per 
cent,  of  hydrobromic  acid.  Assay  this  by  means  of  normal  volume- 
tric solution  of  soda,  and  add  distilled  water  until  it  shall  have  the 
strength  of  34  per  cent,  of  hydrobromic  acid.  The  product  will  weigh 
about  eleven  parts,  and  the  loss  of  hydrobromic  acid  as  calculated  from 
the  potassium  bromide  will  be  about  1*2  per  cent. 
Solution  of  hydrobromic  acid  thus  prepared  is  a  limpid,  colorless, 
odorless  liquid,  having  a  strongly  acid  taste.  At  i5,6°C.=6o°F.  it 
has  a  s.  g.  of  1*274.    At  25°C.=77°F.  the  s.  g.  is  1*257  both  com- 
