Am.  Jour.  Pharm. 
Oct.,  1918. 
Dissolving  Zinc  Chloride. 
713 
rod,  until  a  point  was  reached  when  a  drop  gave  a  turbidity  with 
water.  This  stage  was  not  attained  until  after  and  in  succession  the 
last  trace  of  moisture  which  had  been  held  so  tenaciously  by  the  zinc 
chloride  and  the  adhering  hydrochloric  acid  had  been  driven  off  and 
the  zinc  chloride  had  been  liquefied  by  the  heat,  giving  additional  evi- 
dence that  adhering  hydrochloric  acid  had  been  the  reason  for  this 
syrupy  liquid  persistently  dissolving  clear.  The  fused  residue  was 
now  treated  with  an  abundance  of  water  and  the  mixture  filtered. 
This  filtrate  was  evaporated  to  a  syrupy  condition  as  before  and 
found  to  dissolve  clear  in  water.  Another  fused  mass  correspond- 
ing to  that  just  described  was  treated  with  a  limited  quantity  of 
water  and  upon  filtering,  evaporating  and  again  diluting,  oxychloride 
separated,  because  when  the  mass  was  treated  with  the  limited  quan- 
tity of  water  not  enough  water  was  present  to  adjust  the  acidity  so 
that  the  full  production  of  oxychloride  might  take  place.  The  in- 
soluble portions  of  the  fused  masses  were  all  shown  by  tests  to  be 
oxychloride. 
In  order  to  observe  a  specimen  of  zinc  chloride  which  had  never 
been  in  a  solid  state  and  thus  avoid  oxychloride  due  to  overheat- 
ing, a  concentrated  solution  was  prepared  by  saturating  warm  hydro- 
chloric acid  with  zinc  oxide  added  in  excess.  The  clear  super- 
natant liquid  from  this  mixture  precipitated  with  both  hot  and  cold 
water  and  in  all  respects  corresponding  dilutions  behaved  exactly  as 
those  obtained  from  the  dissolved  salt.  One  could  imagine  noth- 
ing more  likely  chemically  neutral  than  this  solution  prepared  by 
neutralizing  the  acid  with  the  zinc  base ;  and  its  precipitation  by 
water  must  convince  the  most  skeptical  that  free  acid  is  not  only 
present  in  every  diluted  zinc  chloride  solution  prepared  with  water 
alone  as  the  solvent,  but  also  that  it  is  needed  to  insure  complete 
solution. 
Neutralize  such  diluted  solution  in  part,  and  simultaneously  with 
the  precision  of  natural  law  readjustment  takes  place  between  the 
zinc  chloride  and  the  water  present,  with  the  formation  of  oxy- 
chloride and  the  production  of  a  corresponding  amount  of  free  acid ; 
there  will  be  free  hydrochloric  acid  in  a  diluted  solution  made  with 
water  alone  while  there  is  zinc  chloride  left  in  it. 
Any  amplification  of  these  experiments  jwill  but  reiterate  the 
proven  fact,"  at  first  but  inference — that  when  this  dilution  is  reached 
there  has  been  formed  and  retained  hydrochloric  acid,  and  sufficient 
of  it  to  re-dissolve  the  residue  in  any  amount  of  water  that  may  be 
added. 
