Am.  Jour.  Pharm.  ! 
Jan.,  1894.  J 
The  Action  of  Zinc,  etc. 
49 
after  having  removed  the  potassium  chloride  with  water.  The 
former  method  presents  the  causes  of  error  inherent  in  the  use  of 
weighed  filters.  The  latter  method  is  tedious,  and  involves  the 
successive  incineration  of  two  filters. 
The  following  method  is  very  rapid  and  very  accurate.  The  dou- 
ble chloride,  obtained  in  the  ordinary  manner,  is  washed  with  a 
mixture  of  equal  volumes  of  alcohol  and  anhydrous  ether,  in. 
the  capsule  in  which  it  has  been  produced,  until  the  filtrate  runs 
through  absolutely  colorless — a  result  obtained  with  a  small  volume 
of  the  mixture.  The  residual  salt  is  dissolved  in  boiling  water,  col- 
lecting the  solution  in  a  conical  vessel.  We  add  to  it  a  little  pure 
hydrochloric  acid,  and  introduce  gradually  fragments  of  magnesium 
until  the  liquor  is  completely  decolorized  and  the  magnesium  dis- 
solves without  its  surface  becoming  tarnished. 
The  platinum  thus  deposited  is  very  easy  to  wash,  and  does  not 
adhere  to  the  sides  of  the  capsule.  It  is  brought  upon  a  filter 
without  folds ;  the  filter,  after  desiccation,  is  incinerated  and  the 
platinum  is  ignited.  Its  weight,  multiplied  by  0-3939  or  by  o  4747, 
gives  the  corresponding  weight  of  potassium  or  potassa. 
This  method  is  very  advantageous  in  the  determination  of  potassa 
in  presence  of  soda  and  other  substances,  except  ammoniacal  salts. 
It  is  sufficient  to  substitute  this  method  of  liberating  the  platinum 
for  that  proposed  by  Corenwinder  and  Contamine  in  their  method 
for  the  determination  of  potassa  in  mixtures,  such  as  salines  or 
refined  potash. 
By  the  use  of  magnesium  we  have  obtained  exactly  100  percent, 
of  the  potassa  contained  in  potassium  sulphate  mixed  with  large 
quantities  of  sodium  phosphate  and  sulphate,  calcium,  magnesium, 
and  iron  chloride,  and  aluminum  sulphate,  if  we  employ  for  the 
precipitating  and  washing  the  chloroplatinate  a  mixture  of  equal 
volumes  of  anhydrous  alcohol  and  ether. 
In  presence  of  bromides,  the  precipitate  produced  by  platinum 
chloride  may  contain  more  or  less  bromine  replacing  an  equivalent 
quantity  of  chlorine.  Still,  a  determination  of  the  weight  of  the 
platinum  will  give  in  this  case  an  exact  result. 
We  must  not  forget  to  transform  the  potassium  salts  into  chloride 
if  the  acids  are  volatile,  or,  in  the  contrary  case,  to  acidulate  with 
hydrochloric  acid. — Bull,  de  la  Soc.  Chitn.  de  Paris,  Series  3,  ix  and 
x,  p.  602,  through  Chem.  News,  1893,  264- 
