708 
Dissolving  Zinc  Chloride. 
(  Am.  Tour.  Pharm. 
Oct.,  1 918. 
to  investigate  it,  so  acting  under  the  impression  that  free  hydro- 
chloric acid  would  be  present  in  any  event,  as  shown  by  the  equa- 
tion, we  concluded  that  the  most  practical  thing  to  do  was  to  supply 
that  through  lack  of  which  the  obstacle  arose  ;  in  other  words,  add 
sufficient  hydrochloric  acid  to  the  zinc  chloride  itself  to  enable 
the  water  to  carry  all  of  the  zinc  chloride  into  solution,  realizing 
as  already  said,  that  free  hydrochloric  acid  would  be  present  in  the 
finished  product  whether  all  or  only  part  of  the  zinc  chloride  was  in 
solution,  for  this  procedure  assures  the  zinc  to  the  patient. 
The  addition  of  the  hydrochloric  acid  was  made  in  the  case  of 
several  grains  of  zinc  chloride  by  putting  a  single  drop  of  concen- 
trated acid  upon  the  salt  and  after  mixing  by  trituration  the  water 
was  added.  "When  but  a  grain  or  two  of  zinc  chloride  was  to  be 
dissolved,  a  mere  trace  or  touch  of  the  acid  was  used,  or  portion  of 
a  drop  of  diluted  acid.  Much  less  acid  is  needed  if  put  directly  upon 
the  zinc  salt.  Any  mixture  prepared  without  this  addition  and  show- 
ing turbidity  was  rejected  because  too  much  acid  would  have  to  be 
added  to  the  fluid.  The  effect  of  the  acid  added  is  to  produce  zinc 
chloride  and  water. 
Zn  (OH) CI  +  HC1  =  ZnCL  +  H20, 
the  very  material  desired  in  the  product.  We  have  often  wondered 
"  what  better  can  be  done  ?  "  Theory  would  indicate  that  the  hydro- 
chloric acid  in  the  liquid  could  be  neutralized  by  mixing  it  with  zinc 
oxide  or  carbonate  and  filtering  oft  the  undissolved  portion.  This 
plan  however  is  neither  so  accurate  nor  so  simple  as  it  appears  when 
tried  on  a  small  lot  of  eye  drops. 
Although  the  plan  of  adding  acid  had  been  used  for  many  years, 
without  any  untoward  effects,  there  might  have  arisen  a  comparison 
between  the  work  of  dispensers,  wherein  the  reason  for  such  an  ad- 
dition might  be  difficult  of  explanation  to  the  lay  mind  ;  for  although 
we  believed  we  were  acting  within  the  bounds  of  right  judgment,  it 
might  not  have  been  possible  to  satisfy  the  patient  that  such  was  the 
case.  Xor  was  the  patient  the  only  one  who  might  have  to  be  con- 
vinced of  the  commonsense  of  the  plan,  as  we  shall  soon  learn  ;  and 
it  was  this  apprehension  perhaps,  more  than  any  other  influence,  that 
persuaded  us  to  look  for  another  solvent. 
Since  undertaking  this  study  of  the  subject,  we  find  that  others 
have  practiced  this  method  as  the  only  practical  means  of  dissolving 
zinc  chloride. 
