Am.  Jour.  Pharm. 
Oct.,  1918. 
Dissolving  Zinc  Chloride. 
715 
by  means  of  an  equal  amount  of  boric  acid  are  permanent,  with  the 
exception  of  the  saturated  solution  as  already  mentioned.  Less  than 
an  equal  amount  of  boric  acid  does  not  appear  to  insure  permanency. 
The  limit  of  solubility  of  boric  acid  is  the  only  shortcoming  of 
this  agent  so  far  observed.  It  is  of  interest  to  note  for  subsequent 
comparison,  that  upon  boiling  zinc  oxide  or  zinc  carbonate  and  boric 
acid  together,  no  zinc  enters  solution. 
While  little,  if  any,  objection  can  be  raised  to  the  use  of  boric 
acid  in  this  connection,  yet  because  of  its  limited  effect,  we  sought 
for  another  solvent  less  restricted.  Attention  had  been  arrested  by 
a  reference  to  the  soluble  double  salts  which  zinc  chloride  forms 
with  ammonium  chloride,  and  effort  was  turned  in  that  direction. 
The  results  with  boric  acid  had  strengthened  the  belief  that  an  acidu- 
lated medium  is  essential  to  the  purpose,  and  associating  this  thought 
with  the  fact  that  solutions  of  ammonium  chloride  are  prone  to 
redden  litmus,  unquestionably  through  the  presence  of  a  trace  of 
free  hydrochloric  acid,  it  was  undertaken  to  learn  what  effect  am- 
monium chloride  would  have  in  the  dissolving  of  zinc  chloride. 
Gratifying,  indeed,  was  it  to  find  the  substance  a  very  efficient  sol- 
vent, and  more  powerful  than  boric  acid,  for  applied  directly  to  the 
zinc  chloride  one  grain  of  ammonium  chloride  will  dissolve  five 
grains  of  zinc  chloride.  If  used  to  dissolve  a  precipitate  of  oxy- 
chloride  an  additional  amount  may  be  needed,  apparently  dependent 
on  strength  of  solution.  The  solutions  with  ammonium  chloride  are 
permanent. 
There  would  seem  to  be  no  objection  to  the  use  of  the  few  grains 
of  ammonium  chloride  which  would  be  needed  to  prepare  an  appli- 
cation for  a  mucus  membrane  since  such  parts  are  constantly  satu- 
rated with  solution  of  chlorides  and  likewise  inured  -to  the  presence 
of  ammonium  compounds.  Should  a  very  strong  solution  of  zinc 
chloride  be  needed  as  for  powerful  local  effect,  ammonium  chloride 
may  be  depended  upon  to  yield  a  clear  solution. 
The  possibility  of  decomposing  ammonium  chloride  in  solution, 
with  zinc  oxide,  in  the  capacity  of  an  alkali  and  alkaline  earth,  had 
not  come  to  mind  until  now.  Upon  boiling  zinc  oxide  with  a  solu- 
tion of  ammonium  chloride  it  was  found  that  the  zinc  oxide  dis- 
solved, of  course,  with  the  inevitable  liberation  of  ammonia.  Zinc 
carbonate  behaves  in  this  same  manner  with  ammonium  chloride. 
A  parallel  test  with  water  was  made  to  check  up  these  results  against 
any  soluble  zinc  impurities  in  the  oxide  and  carbonate.    Herein  may 
