7io 
Dissolving  Zinc  Chloride. 
Am.  Jour.  Pharm. 
Oct.,  1918. 
to  many  of  the  soluble  salts  of  the  metals ;  we  merely  want  to  remind 
ourselves  at  this  time  that  it  does  not  indicate  free  acid.  The  sample 
of  zinc  chloride  which  was  employed  for  these  experiments  con- 
formed to  the  U.  S.  P.  requirements  as  to  limit  of  oxychloride  con- 
tent and  production ;  it  also  conformed  to  the  other  tests  of  the 
same  standard.  After  a  number  of  experiments  made  more  or  less 
at  random  to  determine  features  which  seem  to  have  bearing  upon 
the  matter  in  hand,  a  series  of  experiments  was  outlined  through 
which  it  was  purposed  to  follow  some  zinc  chloride  in  order  to 
note  its  behavior  under  varying  conditions. 
Accordingly,  a  convenient  portion  of  it  was  placed  in  a  vessel 
and  water  added  drop  by  drop  with  constant  stirring.  Approxi- 
mately an  equal  weight  of  water  dissolved  it — the  mixture  becoming 
warm  as  solution  progressed — and  a  practically  clear  solution  re- 
sulted. The  addition  of  water  in  small  portions  was  continued  until 
a  decided  precipitate  made  its  appearance.  These  experiments  were 
repeated  several  times  with  different  amounts  of  zinc  chloride.  On 
an  average  it  required  over  five  times  as  much  water  as  zinc  chloride 
to  produce  a  permanent  turbidity  or  precipitate.  The  further  dilu- 
tion of  these  turbid  solutions  with  water,  threw  out  more  precipi- 
tate, so  the  addition  of  water  was  continued  until  to  all  appearances 
no  more  oxychloride  was  being  produced.  This  condition  appeared 
to  be  attained  when  twenty  or  more  parts  of  water  had  been  added. 
One  of  these  mixtures  was  allowed  to  settle  and  the  clear  super- 
natant liquid  decanted  upon  asbestos  wool.  The  filtrate  was  placed 
upon  a  water  bath  for  evaporation.  The  undissolved  portion  (oxy- 
chloride) was  washed  and  boiled  with  sodium  carbonate  to  separate 
the  zinc  and  chlorine,  both  of  which  were  shown  to  be  present. 
Before  passing  on  to  the  consideration  of  the  evaporated  filtrate 
let  us  observe  some  of  the  behaviors  of  the  clear  solution  of  equal 
parts  of  zinc  chloride  and  water.  The  statement  is  common  in 
works  of  reference  that  zinc  oxychloride  is  dissolved  by  zinc  chloride 
solution ;  now  the  fact,  that  up  to  a  certain  dilution  a  clear  solution 
of  zinc  chloride  is  possible  must  certainly  be  conceded  to  be  proof 
of  this  statement. 
The  inference  then  would  be  that  the  total  acidity  of  the  zinc 
chloride  solution  is  sufficiently  powerful  in  that  certain  concentra- 
tion to  hold  in  solution  any  oxychloride  which  existed  in  the  sample 
as  well  as  to  prevent  the  separation  of  the  incipient  oxychloride 
which  will  be  manifested  upon  a  further  dilution. 
