A^f  Jour.  Phaem.  \ 
Nov.  1, 1872,  j 
Laboratory  Notes. 
493 
^LABORATORY  NOTES  * 
By  Edward  Smith,  F.C.S. 
Bromide  of  Potassium. — This  salt  is  generally  found  in  commerce 
of  a  high  degree  of  purity.  This  is  not,  however,  always  the  case  ;  a 
sample  sent  to  me  proved  to  be  contaminated  with  chloride  of  potas- 
sium. The  amount  of  chloride  was  estimated  as  follows,  iodides,  io- 
dates,  and  carbonates  having  been  previously  ascertained  to  be  ab- 
sent : 
•0640  grains  of  the  dry  salt  were  titrated  with7^  solution  of  silver 
nitrate,  potassium  chromate  as  indicator,  55*5  c.  c.  of  Tqq  silver  were- 
required  to  complete  the  reaction,  and 
55*5  x  '00119  =  -0660 ;  the  volume  of  silver  solution  used  is  there- 
fore in  excess  of  that  required  for  pure  potassium  bromide,  for  *0640- 
(amount  taken)  should  require  53*78  c.  c,  since  *0640  -f-  -00119  = 
53-78  and 
51-0  c.  c.  Tj„  silver  x  -00119  =  -06069  K  Br. 
4-5  c.  c.  7  ^  silver  x  -000745  =  -00335  KC1. 
55-5  c.  c.  =  -06404  K  Br.  +  K  CI. 
and  -00335      -0640  x  100  =  5-20 
•06069  -f-  -0640  x  100  =94-80 
The  sample,  therefore,  contained  5-2  per  cent,  of  chloride  and  94*8 
per  cent,  of  bromide  of  potassium. 
Acetic  Acid. — Iron  is  not  usually  mentioned  in  the  text-books  as 
an  impurity  in  this  acid.  A  small  amount  of  iron  proves  very  tire- 
some, since,  if  the  acid  be  used  for  preparing  mindererus,  the  iron  is 
constantly  and  gradually  depositing.  On  examining  some  acid  which 
had  been  partly  used  in  making  mindererus,  I  found  it  to  contain  iron 
and  manganese,  the  proportion  of  the  former  metal  was  2-67  grains 
to  an  imperial  pint.  The  manganese  was  not  estimated,  but  was  very 
readily  detected  in  the  iron  sulphide  (thrown  down  by  ammonium  sul- 
phide from  the  neutralized  acid)  before  the  blow-pipe.  In  every  other 
respect  the  acid  was  satisfactory. 
Glycerin. — The  high  price  of  English  glycerin  has  encouraged  the 
introduction  of  foreign  supplies.  English  glycerin,  as  a  rule,  stands 
the  Pharmacopoeia  tests  of  gravity,  etc.,  well.    Continental  samples, 
*  Read  at  the  Brighton  meeting  of  the  British  Pharmaceutical  Conference, 
August  14,  1872. 
