76 
Syrup  of  Bromide  of  Zinc, 
(  Am.  Jour.  Pharm. 
t      Feb.,  1880. 
The  disadvantages  of  manipulating  with  free  bromine  are  obvious. 
In  the  second  process  the  hydrobromic  acid  solution  is  not  easily  obtained 
by  all  pharmacists,  nor  are  they  all  supplied  with  the  conveniences  for 
making  the  acid. 
For  these  reasons  experiments  were  performed  in  the  College  Labor- 
atory with  the  view  of  obtaining  a  formula  whereby  pharmacists  could 
make,  from  materials  always  on  hand,  a  solution  of  bromide  of  zinc 
for  the  purpose  of  making  the  syrup  of  bromide  of  zinc. 
The  following  process  depends  upon  the  double  decomposition  of 
bromide  of  potassium  and  sulphate  of  zinc. 
The  quantities  used  were  taken  according  to  the  proportion  existing 
between  the  molecular  weights  of  the  salts,  which  is  about  5  to  6,  or 
2  molecules  of  bromide  of  potassium  (238)  to  i  of  crystallized  sul- 
phate of  zinc  (287).  2KBr+ZnSO,-=ZnBr2+K.SO,. 
Experiment  I.  35  grains  of  potassium  bromide  and  42  grains  of  crys- 
tallized sulphate  of  zinc  were  triturated  in  a  mortar,  and  after  the  mix- 
ture had  become  liquid  alcohol  was  added  to  dissolve  the  resulting 
ZnBr^.  The  solution  was  then  filtered  from  the  crystalline  precipitate; 
the  zinc  was  precipitated  by  sulphhydrate  of  ammonium,  filtered,  the 
filtrate  evaporated  to  dryness,  and  a  residue  was  obtained  which  was 
found  to  be  bromide  of  potassium.  The  precipitate  obtained  by  alco- 
hol was  washed  with  alcohol,  and  then  contained  the  sulphates  of  both 
cnetals,  but  was  free  from  bromide. 
Experiment  II.  100  grains  of  potassium  bromide  and  120  grains  of 
crystallized  sulphate  of  zinc  were  dissolved  separately  in  a  small  quan- 
tity of  water,  and  the  solutions  mixed  while  hot.  When  the  liquor 
was  cold,  twice  the  bulk  of  alcohol  was  added,  the  precipitate  removed 
by  filtration,  and  the  filtrate  treated  the  same  as  in  experiment  I.  In 
this  also,  was  found  a  large  percentage  of  bromide  of  potassium. 
These  experiments  were  repeated,  and  with  the  same  results. 
It  necessarily  followed  that  either  the  process  or  the  manipulation 
was  faulty. 
Iodide  of  zinc  in  the  presence  of  any  of  the  iodides  of  the  alkaline 
metals  forms  a  double  salt. 
As  iodine  and  bromine  act  similarly  in  combining,  the  conclusion  is 
that  in  the  above  experiments  the  double  salt,  KBrZnBr2,  was  formed. 
In  order  to  decompose  this  double  salt,  a  larger  quantity  of  zinc  sul- 
phate must  be  used.    The  quantity  was  doubled,  as  follows: 
